diff --git a/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/Examples.tsx b/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/Examples.tsx
index bcc3301f1e8..7bf53f93db6 100644
--- a/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/Examples.tsx
+++ b/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/Examples.tsx
@@ -1,4 +1,5 @@
 import ComponentBox from '../../../../../../shared/tags/ComponentBox'
+import { createMinimumAgeValidator } from '@dnb/eufemia/src/extensions/forms/Field/NationalIdentityNumber'
 import { Field } from '@dnb/eufemia/src/extensions/forms'
 
 export const Empty = () => {
@@ -188,3 +189,51 @@ export const ValidationExtendValidator = () => {
     </ComponentBox>
   )
 }
+
+export const ValidationExtendValidatorAdult = () => {
+  return (
+    <ComponentBox scope={{ createMinimumAgeValidator }}>
+      {() => {
+        const adultValidator = createMinimumAgeValidator(18)
+        const myAdultValidator = (value, { validators }) => {
+          const { dnrAndFnrValidator } = validators
+
+          return [dnrAndFnrValidator, adultValidator]
+        }
+
+        return (
+          <Field.NationalIdentityNumber
+            required
+            value="56052459244"
+            onBlurValidator={myAdultValidator}
+            validateInitially
+          />
+        )
+      }}
+    </ComponentBox>
+  )
+}
+
+export const ValidationFnrAdult = () => {
+  return (
+    <ComponentBox scope={{ createMinimumAgeValidator }}>
+      {() => {
+        const adultValidator = createMinimumAgeValidator(18)
+        const myFnrAdultValidator = (value, { validators }) => {
+          const { fnrValidator } = validators
+
+          return [fnrValidator, adultValidator]
+        }
+
+        return (
+          <Field.NationalIdentityNumber
+            required
+            value="49100651997"
+            onBlurValidator={myFnrAdultValidator}
+            validateInitially
+          />
+        )
+      }}
+    </ComponentBox>
+  )
+}
diff --git a/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/demos.mdx b/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/demos.mdx
index 2d20256438d..446131cc0b7 100644
--- a/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/demos.mdx
+++ b/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/demos.mdx
@@ -54,18 +54,28 @@ Below is an example of the error message displayed when there's an invalid Norwe
 
 It validates [D numbers](https://www.skatteetaten.no/en/person/national-registry/identitetsnummer/d-nummer/) using the [fnrvalidator](https://github.com/navikt/fnrvalidator).
 
-Below is an example of the error message displayed when there's an invalid D number:
+Below is an example of the error message displayed when there's an invalid D number(a D number has its first number in the identification number increased by 4):
 
 <Examples.ValidationDnr />
 
 ### Validation function
 
-You can provide your own validation function.
+You can provide your own validation function, either to `validator` or `onBlurValidator`.
 
 <Examples.ValidationFunction />
 
 ### Extend validation with custom validation function
 
-You can [extend the existing validations](/uilib/extensions/forms/create-component/useFieldProps/info/#validators)(`dnrValidator`, `fnrValidator`, and `dnrAndFnrValidator`) with your own validation function.
+You can [extend the existing validations](/uilib/extensions/forms/create-component/useFieldProps/info/#validators)(`dnrValidator`, `fnrValidator`, `dnrAndFnrValidator`, and make your own age validator by using the `createMinimumAgeValidator` function) with your own validation function.
 
 <Examples.ValidationExtendValidator />
+
+### Extend validation with adult validator
+
+You can [extend the existing validations](/uilib/extensions/forms/create-component/useFieldProps/info/#validators)(`dnrValidator`, `fnrValidator`, and `dnrAndFnrValidator`) with your own age validator, by using the `createMinimumAgeValidator` function.
+
+<Examples.ValidationExtendValidatorAdult />
+
+### Validate only national identity numbers(fnr) above 18 years old
+
+<Examples.ValidationFnrAdult />
diff --git a/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/properties.mdx b/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/properties.mdx
index 694c8830f82..4cd7b9dc2e4 100644
--- a/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/properties.mdx
+++ b/packages/dnb-design-system-portal/src/docs/uilib/extensions/forms/feature-fields/NationalIdentityNumber/properties.mdx
@@ -21,12 +21,25 @@ import { NationalIdentityNumberProperties } from '@dnb/eufemia/src/extensions/fo
 
 `Field.NationalIdentityNumber` expose the following validators through its `validator` and `onBlurValidator` property:
 
-- `dnrValidator`: validates a d number.
+- `dnrValidator`: validates a D number.
 - `fnrValidator`: validates a national identity number (fødselsnummer).
 - `dnrAndFnrValidator`:
-  - validates the identification number as a d number when first digit is 4 or greater (because a d number has its first number increased by 4).
+  - validates the identification number as a D number when first digit is 4 or greater (because a D number has its first number increased by 4).
   - validates the identification number as a national identity number (fødselsnummer) when first digit is 3 or less.
 
+You can create your own age validator by using the `createMinimumAgeValidator` function. It takes an age as a parameter and returns a validator function. The validator function takes a value and returns an error message if the value is not above the given age.
+It validates if the identification number has a date of birth that is 18 years or older. It uses only the 7 first digits of the identification number to validate. The first 6 digits representing the birth of date, and the next digit represents the century.
+As it only use the 7 first digits, it does not validate the identification number, therefore it's quite common to use this validator together with one of the validators above (`dnrValidator`, `fnrValidator` or `dnrAndFnrValidator`) to validate the identification number as well.
+
+You need to import the `createMinimumAgeValidator` function from the `Field.NationalIdentityNumber` component:
+
+```tsx
+import { createMinimumAgeValidator } from '@dnb/eufemia/extensions/forms/Field/NationalIdentityNumber'
+
+// Create a validator that validates if the value is above 18 years old
+const above18YearsValidator = createMinimumAgeValidator(18)
+```
+
 See the following [example](/uilib/extensions/forms/feature-fields/NationalIdentityNumber/#extend-validation-with-custom-validation-function) on how to extend validation using the exposed validators.
 
 ## Translations
diff --git a/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/NationalIdentityNumber.tsx b/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/NationalIdentityNumber.tsx
index 5e3420b525f..277f1f3419f 100644
--- a/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/NationalIdentityNumber.tsx
+++ b/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/NationalIdentityNumber.tsx
@@ -1,7 +1,7 @@
 import React, { useCallback, useMemo } from 'react'
 import StringField, { Props as StringFieldProps } from '../String'
 import { dnr, fnr } from '@navikt/fnrvalidator'
-import { Validator } from '../../types'
+import { FormError, Validator } from '../../types'
 
 import useErrorMessage from '../../hooks/useErrorMessage'
 import useTranslation from '../../hooks/useTranslation'
@@ -14,18 +14,28 @@ export type Props = Omit<StringFieldProps, 'onBlurValidator'> & {
 
 function NationalIdentityNumber(props: Props) {
   const translations = useTranslation().NationalIdentityNumber
-  const { label, errorRequired, errorFnr, errorDnr } = translations
+  const {
+    label,
+    errorRequired,
+    errorFnr,
+    errorDnr,
+    errorMinimumAgeValidator,
+  } = translations
   const errorMessages = useErrorMessage(props.path, props.errorMessages, {
     required: errorRequired,
     pattern: errorFnr,
     errorFnr,
     errorDnr,
+    errorMinimumAgeValidator,
   })
 
   const fnrValidator = useCallback(
     (value: string) => {
-      // have to check for undefined as @navikt/fnrvalidator does not support undefined
-      if (value !== undefined && fnr(value).status === 'invalid') {
+      if (
+        value !== undefined &&
+        (Number.parseInt(value.substring(0, 1)) > 3 ||
+          fnr(value).status === 'invalid')
+      ) {
         return Error(errorFnr)
       }
     },
@@ -34,8 +44,11 @@ function NationalIdentityNumber(props: Props) {
 
   const dnrValidator = useCallback(
     (value: string) => {
-      // have to check for undefined as @navikt/fnrvalidator does not support undefined
-      if (value !== undefined && dnr(value).status === 'invalid') {
+      if (
+        value !== undefined &&
+        (Number.parseInt(value.substring(0, 1)) < 4 ||
+          dnr(value).status === 'invalid')
+      ) {
         return Error(errorDnr)
       }
     },
@@ -106,5 +119,64 @@ function NationalIdentityNumber(props: Props) {
   return <StringField {...StringFieldProps} />
 }
 
+export function getAgeByBirthDate(birthDate: Date): number {
+  const today = new Date()
+  const age = today.getFullYear() - birthDate.getFullYear()
+  const month = today.getMonth() - birthDate.getMonth()
+  const day = today.getDate() - birthDate.getDate()
+
+  if (month < 0 || (month === 0 && day < 0)) {
+    return age - 1
+  }
+
+  return age
+}
+
+export function getBirthDateByFnrOrDnr(value: string) {
+  if (value === undefined) {
+    return // stop here
+  }
+
+  const yearPart = value.substring(4, 6)
+  const centuryNumber = Number.parseInt(value.substring(6, 7))
+
+  const isBornIn20XX = centuryNumber >= 5
+  const year = isBornIn20XX ? `20${yearPart}` : `19${yearPart}`
+  const month = Number.parseInt(value.substring(2, 4))
+
+  const differentiatorValue =
+    value.length > 0 ? Number.parseInt(value.substring(0, 1)) : undefined
+  const isDnr = differentiatorValue && differentiatorValue > 3
+
+  const day = isDnr
+    ? Number.parseInt(value.substring(0, 2)) - 40
+    : Number.parseInt(value.substring(0, 2))
+
+  return new Date(Number.parseInt(year), month - 1, day)
+}
+
+export function createMinimumAgeValidator(age: number) {
+  return (value: string) => {
+    if (typeof value !== 'string') {
+      return // stop here
+    }
+
+    if (value.length > 6) {
+      const date = getBirthDateByFnrOrDnr(value)
+      if (getAgeByBirthDate(date) >= age) {
+        return // stop here
+      }
+    }
+
+    return new FormError(
+      'NationalIdentityNumber.errorMinimumAgeValidator',
+      {
+        validationRule: 'errorMinimumAgeValidator', // "validationRule" Will be removed in future PR
+        messageValues: { age: String(age) },
+      }
+    )
+  }
+}
+
 NationalIdentityNumber._supportsSpacingProps = true
 export default NationalIdentityNumber
diff --git a/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/__tests__/NationalIdentityNumberAdultValidator.test.tsx b/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/__tests__/NationalIdentityNumberAdultValidator.test.tsx
new file mode 100644
index 00000000000..17f7605768d
--- /dev/null
+++ b/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/__tests__/NationalIdentityNumberAdultValidator.test.tsx
@@ -0,0 +1,668 @@
+import React from 'react'
+import { render, waitFor, screen } from '@testing-library/react'
+import { Field, Validator } from '../../..'
+import { createMinimumAgeValidator } from '../NationalIdentityNumber'
+
+import nbNO from '../../../constants/locales/nb-NO'
+
+const nb = nbNO['nb-NO']
+
+describe('Field.NationalIdentityNumber with adultValidator', () => {
+  const errorMinimumAgeValidator =
+    nb.NationalIdentityNumber.errorMinimumAgeValidator.replace(
+      '{age}',
+      '18'
+    )
+  const adultValidator = createMinimumAgeValidator(18)
+  const extendingDnrAndFnrValidatorWithAdultValidator: Validator<
+    string
+  > = (value, { validators }) => {
+    const { dnrAndFnrValidator } = validators
+
+    return [dnrAndFnrValidator, adultValidator]
+  }
+
+  const extendingDnrValidatorWithAdultValidator: Validator<string> = (
+    value,
+    { validators }
+  ) => {
+    const { dnrValidator } = validators
+
+    return [dnrValidator, adultValidator]
+  }
+
+  const extendingFnrValidatorWithAdultValidator: Validator<string> = (
+    value,
+    { validators }
+  ) => {
+    const { fnrValidator } = validators
+
+    return [fnrValidator, adultValidator]
+  }
+
+  const myAdultValidator: Validator<string> = () => {
+    return [adultValidator]
+  }
+
+  it('should display error if required and validateInitially', async () => {
+    render(
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultValidator}
+        required
+        validateInitially
+      />
+    )
+
+    await waitFor(() => {
+      expect(screen.queryByRole('alert')).toBeInTheDocument()
+      expect(screen.queryByRole('alert')).toHaveTextContent(
+        nb.NationalIdentityNumber.errorRequired
+      )
+    })
+  })
+
+  it('should display error when value is invalid', async () => {
+    render(
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultValidator}
+        validateInitially
+        value="123"
+      />
+    )
+
+    await waitFor(() => {
+      expect(screen.queryByRole('alert')).toBeInTheDocument()
+      expect(screen.queryByRole('alert')).toHaveTextContent(
+        errorMinimumAgeValidator
+      )
+    })
+  })
+
+  it('should not display error when validateInitially and no value', async () => {
+    render(
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultValidator}
+        validateInitially
+      />
+    )
+
+    await expect(() => {
+      expect(screen.queryByRole('alert')).toBeInTheDocument()
+    }).neverToResolve()
+  })
+
+  describe('should validate if identity numbers is adult(18 years and older)', () => {
+    jest.useFakeTimers().setSystemTime(new Date('2024-10-09').getTime())
+    const fnr0YearsOld = [
+      '10072476609',
+      '29082499936',
+      '03022450718',
+      '11032455001',
+      '30082489912',
+    ]
+
+    const fnr17YearsOld = [
+      '31050752669',
+      '10040752779',
+      '28050772596',
+      '25060798446',
+      '07100782566',
+      '08100787300',
+    ]
+
+    const fnrUnder18YearsOld = [...fnr0YearsOld, ...fnr17YearsOld]
+
+    const fnr18Years = [
+      '09100654021',
+      '09100696336',
+      '24040664900',
+      '26020682328',
+      '07070663990',
+      '11030699302',
+      '31010699021',
+    ]
+    const fnr99Years = [
+      '14102535759',
+      '20042528022',
+      '14082523414',
+      '01022537632',
+      '01022504416',
+    ]
+    const fnr18YearsOldTo99 = [
+      '25047441741',
+      '06118836551',
+      '19042648291',
+      '18053526132',
+      '29075642618',
+    ]
+    const fnr99To120YearsOld = [
+      '22041330302',
+      '02061234694',
+      '23020704845',
+      '28021741177',
+      '10121933999',
+    ]
+    const fnr18YearsOldAndOlder = [
+      ...fnr18Years,
+      ...fnr99Years,
+      ...fnr18YearsOldTo99,
+      ...fnr99To120YearsOld,
+    ]
+
+    const dnrUnder18YearsOld = [
+      '42011660597',
+      '44011957371',
+      '45010886213',
+      '60050972871',
+      '65052062378',
+      '70121275293',
+      '71072354979',
+      '43072496079',
+      '44052351836',
+      '56052459244',
+      '59082354829',
+      '63032486179',
+      '48100754692',
+    ]
+    const dnr18YearsOldAndOlder = [
+      '49100651997',
+      '49100697466',
+      '41070663889',
+      '42020653633',
+      '41012413597',
+      '41062421922',
+      '41080422588',
+      '44081020024',
+      '71081924796',
+      '60067139081',
+      '60075812380',
+    ]
+
+    const validIds = [...fnr18YearsOldAndOlder, ...dnr18YearsOldAndOlder]
+
+    const invalidIds = [...fnrUnder18YearsOld, ...dnrUnder18YearsOld]
+
+    const invalidDnums = ['69020112345', '690']
+    const invalidFnrs = ['29020112345', '290']
+
+    describe('when provided as the only validator validation function', () => {
+      it.each(validIds)(
+        'Identity number is 18 years or older : %s',
+        async (validId) => {
+          render(
+            <Field.NationalIdentityNumber
+              validator={myAdultValidator}
+              onBlurValidator={false}
+              validateInitially
+              value={validId}
+            />
+          )
+
+          await expect(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+          }).neverToResolve()
+        }
+      )
+
+      it.each(invalidIds)(
+        'Invalid identity number is not 18 years or older: %s',
+        async (invalidId) => {
+          render(
+            <Field.NationalIdentityNumber
+              validator={myAdultValidator}
+              onBlurValidator={false}
+              validateInitially
+              value={invalidId}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              errorMinimumAgeValidator
+            )
+          })
+        }
+      )
+    })
+
+    describe('when provided as the only onBlurValidation validation function', () => {
+      it.each(validIds)(
+        'Identity number is 18 years or older : %s',
+        async (validId) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={myAdultValidator}
+              validateInitially
+              value={validId}
+            />
+          )
+
+          await expect(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+          }).neverToResolve()
+        }
+      )
+
+      it.each(invalidIds)(
+        'Invalid identity number is not 18 years or older: %s',
+        async (invalidId) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={myAdultValidator}
+              validateInitially
+              value={invalidId}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              errorMinimumAgeValidator
+            )
+          })
+        }
+      )
+    })
+
+    describe('when extending the dnrAndFnrValidator as validator', () => {
+      it.each(validIds)(
+        'Identity number is 18 years or older : %s',
+        async (validId) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingDnrAndFnrValidatorWithAdultValidator}
+              validateInitially
+              value={validId}
+            />
+          )
+
+          await expect(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+          }).neverToResolve()
+        }
+      )
+
+      it.each(invalidIds)(
+        'Invalid identity number is not 18 years or older: %s',
+        async (invalidId) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingDnrAndFnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidId}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              errorMinimumAgeValidator
+            )
+          })
+        }
+      )
+
+      it.each(invalidDnums)(
+        'Invalid identity number is not 18 years or older: %s',
+        async (invalidDnum) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingDnrAndFnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidDnum}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              nb.NationalIdentityNumber.errorDnr
+            )
+          })
+        }
+      )
+
+      it.each(invalidFnrs)(
+        'Invalid identity number is not 18 years or older: %s',
+        async (invalidFnr) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingDnrAndFnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidFnr}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              nb.NationalIdentityNumber.errorFnr
+            )
+          })
+        }
+      )
+    })
+
+    describe('when extending the dnrAndFnrValidator as onBlurValidator', () => {
+      it.each(validIds)(
+        'Identity number is 18 years or older : %s',
+        async (validId) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={
+                extendingDnrAndFnrValidatorWithAdultValidator
+              }
+              validateInitially
+              value={validId}
+            />
+          )
+
+          await expect(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+          }).neverToResolve()
+        }
+      )
+
+      it.each(invalidIds)(
+        'Invalid identity number is not 18 years or older: %s',
+        async (invalidId) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={
+                extendingDnrAndFnrValidatorWithAdultValidator
+              }
+              validateInitially
+              value={invalidId}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              errorMinimumAgeValidator
+            )
+          })
+        }
+      )
+
+      it.each(invalidDnums)(
+        'Invalid identity number is not 18 years or older: %s',
+        async (invalidDnum) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={
+                extendingDnrAndFnrValidatorWithAdultValidator
+              }
+              validateInitially
+              value={invalidDnum}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              nb.NationalIdentityNumber.errorDnr
+            )
+          })
+        }
+      )
+
+      it.each(invalidFnrs)(
+        'Invalid identity number is not 18 years or older: %s',
+        async (invalidFnr) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={
+                extendingDnrAndFnrValidatorWithAdultValidator
+              }
+              validateInitially
+              value={invalidFnr}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              nb.NationalIdentityNumber.errorFnr
+            )
+          })
+        }
+      )
+    })
+
+    describe('when extending the dnrValidator as validator', () => {
+      it.each(dnr18YearsOldAndOlder)(
+        'D number is 18 years or older : %s',
+        async (validDnum) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingDnrValidatorWithAdultValidator}
+              validateInitially
+              value={validDnum}
+            />
+          )
+
+          await expect(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+          }).neverToResolve()
+        }
+      )
+
+      it.each(dnrUnder18YearsOld)(
+        'D number is not 18 years or older: %s',
+        async (invalidDnum) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingDnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidDnum}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              errorMinimumAgeValidator
+            )
+          })
+        }
+      )
+
+      it.each([...invalidDnums, ...invalidFnrs, ...fnr18YearsOldAndOlder])(
+        'Invalid d number: %s',
+        async (invalidDnum) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingDnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidDnum}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              nb.NationalIdentityNumber.errorDnr
+            )
+          })
+        }
+      )
+    })
+
+    describe('when extending the dnrValidator as onBlurValidator', () => {
+      it.each(dnr18YearsOldAndOlder)(
+        'D number is 18 years or older : %s',
+        async (validDnum) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={extendingDnrValidatorWithAdultValidator}
+              validateInitially
+              value={validDnum}
+            />
+          )
+
+          await expect(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+          }).neverToResolve()
+        }
+      )
+
+      it.each(dnrUnder18YearsOld)(
+        'D number is not 18 years or older: %s',
+        async (invalidDnum) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={extendingDnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidDnum}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              errorMinimumAgeValidator
+            )
+          })
+        }
+      )
+
+      it.each([
+        ...invalidDnums,
+        ...invalidFnrs,
+        ...fnr18YearsOldAndOlder,
+        ...fnrUnder18YearsOld,
+      ])('Invalid d number: %s', async (invalidDnum) => {
+        render(
+          <Field.NationalIdentityNumber
+            onBlurValidator={extendingDnrValidatorWithAdultValidator}
+            validateInitially
+            value={invalidDnum}
+          />
+        )
+        await waitFor(() => {
+          expect(screen.queryByRole('alert')).toBeInTheDocument()
+          expect(screen.queryByRole('alert')).toHaveTextContent(
+            nb.NationalIdentityNumber.errorDnr
+          )
+        })
+      })
+    })
+
+    describe('when extending the fnrValidator as validator', () => {
+      it.each(fnr18YearsOldAndOlder)(
+        'Identity number(fnr) is 18 years or older : %s',
+        async (validFnr) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingFnrValidatorWithAdultValidator}
+              validateInitially
+              value={validFnr}
+            />
+          )
+
+          await expect(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+          }).neverToResolve()
+        }
+      )
+
+      it.each(fnrUnder18YearsOld)(
+        'Identity number(fnr) is not 18 years or older: %s',
+        async (invalidFnr) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingFnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidFnr}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              errorMinimumAgeValidator
+            )
+          })
+        }
+      )
+
+      it.each([...invalidFnrs, ...invalidDnums, ...dnr18YearsOldAndOlder])(
+        'Invalid identity number(fnr): %s',
+        async (invalidFnr) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={false}
+              validator={extendingFnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidFnr}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              nb.NationalIdentityNumber.errorFnr
+            )
+          })
+        }
+      )
+    })
+
+    describe('when extending the fnrValidator as onBlurValidator', () => {
+      it.each(fnr18YearsOldAndOlder)(
+        'Identity number(fnr) is 18 years or older : %s',
+        async (validFnr) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={extendingFnrValidatorWithAdultValidator}
+              validateInitially
+              value={validFnr}
+            />
+          )
+
+          await expect(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+          }).neverToResolve()
+        }
+      )
+
+      it.each(fnrUnder18YearsOld)(
+        'Identity number(fnr) is not 18 years or older: %s',
+        async (invalidFnr) => {
+          render(
+            <Field.NationalIdentityNumber
+              onBlurValidator={extendingFnrValidatorWithAdultValidator}
+              validateInitially
+              value={invalidFnr}
+            />
+          )
+          await waitFor(() => {
+            expect(screen.queryByRole('alert')).toBeInTheDocument()
+            expect(screen.queryByRole('alert')).toHaveTextContent(
+              errorMinimumAgeValidator
+            )
+          })
+        }
+      )
+
+      it.each([
+        ...invalidFnrs,
+        ...invalidDnums,
+        ...dnr18YearsOldAndOlder,
+        ...dnrUnder18YearsOld,
+      ])('Invalid identity number(fnr): %s', async (invalidFnr) => {
+        render(
+          <Field.NationalIdentityNumber
+            onBlurValidator={extendingFnrValidatorWithAdultValidator}
+            validateInitially
+            value={invalidFnr}
+          />
+        )
+        await waitFor(() => {
+          expect(screen.queryByRole('alert')).toBeInTheDocument()
+          expect(screen.queryByRole('alert')).toHaveTextContent(
+            nb.NationalIdentityNumber.errorFnr
+          )
+        })
+      })
+    })
+  })
+})
diff --git a/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/stories/NationalIdentityNumber.stories.tsx b/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/stories/NationalIdentityNumber.stories.tsx
index a6870b12bf2..02b55500e24 100644
--- a/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/stories/NationalIdentityNumber.stories.tsx
+++ b/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/stories/NationalIdentityNumber.stories.tsx
@@ -1,16 +1,758 @@
 import React from 'react'
-import { Field } from '../../..'
+import { Field, Validator } from '../../..'
+import { Wrapper } from 'storybook-utils/helpers'
+import { createMinimumAgeValidator } from '../NationalIdentityNumber'
 
 export default {
   title: 'Eufemia/Extensions/Forms/NationalIdentityNumber',
 }
 
-export function NationalIdentityNumber() {
+const simpleValidator = (value) => {
+  return value?.length < 4 ? Error('At least 4 characters') : undefined
+}
+
+const adultValidator = createMinimumAgeValidator(18)
+
+const myAdultValidator: Validator<string> = () => {
+  return [adultValidator]
+}
+
+const myAdultFnrDnrValidator: Validator<string> = (
+  value,
+  { validators }
+) => {
+  const { dnrAndFnrValidator } = validators
+
+  return [dnrAndFnrValidator, adultValidator]
+}
+
+const myFnrValidator: Validator<string> = (value, { validators }) => {
+  const { fnrValidator } = validators
+
+  return [fnrValidator]
+}
+
+const myDnrValidator: Validator<string> = (value, { validators }) => {
+  const { dnrValidator } = validators
+
+  return [dnrValidator]
+}
+
+const myFnrAndDnrValidator: Validator<string> = (
+  value,
+  { validators }
+) => {
+  const { dnrAndFnrValidator } = validators
+
+  return [dnrAndFnrValidator]
+}
+
+export function ValidatorsUndefinedFalse() {
   return (
-    <>
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        validator={undefined}
+        onBlurValidator={false}
+      />
+      <Field.NationalIdentityNumber
+        validator={undefined}
+        onBlurValidator={false}
+        value="123"
+      />
+      <Field.NationalIdentityNumber
+        validator={undefined}
+        onBlurValidator={false}
+        value="12345678901"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={undefined}
+        onBlurValidator={false}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={undefined}
+        onBlurValidator={false}
+        value="123"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={undefined}
+        onBlurValidator={false}
+        value="12345678901"
+      />
+    </Wrapper>
+  )
+}
+
+export function NationalIdentityNumberDefault() {
+  return (
+    <Wrapper>
       <Field.NationalIdentityNumber />
-      <Field.NationalIdentityNumber value="123" />
       <Field.NationalIdentityNumber value="12345678901" />
-    </>
+      <Field.NationalIdentityNumber value="42345678901" />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber validateInitially />
+      <Field.NationalIdentityNumber
+        validateInitially
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        value="42345678901"
+      />
+    </Wrapper>
+  )
+}
+
+export function NationalIdentityNumberAndDNumberOnBlurValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        onBlurValidator={myFnrAndDnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myFnrAndDnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myFnrAndDnrValidator}
+        value="42345678901"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myFnrAndDnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myFnrAndDnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myFnrAndDnrValidator}
+        value="42345678901"
+      />
+    </Wrapper>
+  )
+}
+
+export function NationalIdentityNumberOnBlurValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber onBlurValidator={myFnrValidator} />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myFnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myFnrValidator}
+        value="42345678901"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myFnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myFnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myFnrValidator}
+        value="42345678901"
+      />
+    </Wrapper>
+  )
+}
+
+export function NationalIdentityNumberValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myFnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myFnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myFnrValidator}
+        value="42345678901"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myFnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myFnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myFnrValidator}
+        value="42345678901"
+      />
+    </Wrapper>
+  )
+}
+
+export function DNumberOnBlurValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber onBlurValidator={myDnrValidator} />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myDnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myDnrValidator}
+        value="42345678901"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myDnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myDnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myDnrValidator}
+        value="42345678901"
+      />
+    </Wrapper>
+  )
+}
+
+export function DNumberValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myDnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myDnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myDnrValidator}
+        value="42345678901"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myDnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myDnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myDnrValidator}
+        value="42345678901"
+      />
+    </Wrapper>
+  )
+}
+
+export function AdultOnBlurValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber onBlurValidator={myAdultValidator} />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultValidator}
+        value="123"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultValidator}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultValidator}
+        value="44011957371"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultValidator}
+        value="123"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultValidator}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultValidator}
+        value="44011957371"
+      />
+    </Wrapper>
+  )
+}
+
+export function AdultValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myAdultValidator}
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="123"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="44011957371"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myAdultValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="123"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={false}
+        validator={myAdultValidator}
+        value="44011957371"
+      />
+    </Wrapper>
+  )
+}
+
+export function AdultOnBlurValidatorAndDefaultValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultFnrDnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultFnrDnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultFnrDnrValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultFnrDnrValidator}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={myAdultFnrDnrValidator}
+        value="44011957371"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultFnrDnrValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultFnrDnrValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultFnrDnrValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultFnrDnrValidator}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={myAdultFnrDnrValidator}
+        value="44011957371"
+      />
+    </Wrapper>
+  )
+}
+
+export function AdultValidatorAndDefaultValidator() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+      />
+      <Field.NationalIdentityNumber
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+        value="44011957371"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={myAdultFnrDnrValidator}
+        onBlurValidator={false}
+        value="44011957371"
+      />
+    </Wrapper>
+  )
+}
+
+export function CustomValidatorFunction() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+      />
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="44011957371"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="29082499936"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="44011957371"
+      />
+    </Wrapper>
+  )
+}
+
+export function CustomOnBlurValidatorFunction() {
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber onBlurValidator={simpleValidator} />
+      <Field.NationalIdentityNumber
+        onBlurValidator={simpleValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={simpleValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={simpleValidator}
+        value="321"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={simpleValidator}
+        value="123"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+        value="321"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+        value="123"
+      />
+    </Wrapper>
+  )
+}
+
+export function CustomValidatorFunctionReturnArray() {
+  const validatorX = (value) => {
+    return value?.length < 4 ? Error('At least 4 characters') : undefined
+  }
+
+  const simpleValidator = () => {
+    return [validatorX]
+  }
+
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+      />
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="321"
+      />
+      <Field.NationalIdentityNumber
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="123"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="321"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        validator={simpleValidator}
+        onBlurValidator={false}
+        value="123"
+      />
+    </Wrapper>
+  )
+}
+
+export function CustomOnBlurValidatorFunctionReturnArray() {
+  const validatorX = (value) => {
+    return value?.length < 4 ? Error('At least 4 characters') : undefined
+  }
+
+  const simpleValidator = () => {
+    return [validatorX]
+  }
+
+  return (
+    <Wrapper>
+      <Field.NationalIdentityNumber onBlurValidator={simpleValidator} />
+      <Field.NationalIdentityNumber
+        onBlurValidator={simpleValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={simpleValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={simpleValidator}
+        value="321"
+      />
+      <Field.NationalIdentityNumber
+        onBlurValidator={simpleValidator}
+        value="123"
+      />
+      <h2>Validate Initially:</h2>
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+        value="12345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+        value="42345678901"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+        value="321"
+      />
+      <Field.NationalIdentityNumber
+        validateInitially
+        onBlurValidator={simpleValidator}
+        value="123"
+      />
+    </Wrapper>
   )
 }
diff --git a/packages/dnb-eufemia/src/extensions/forms/constants/locales/en-GB.ts b/packages/dnb-eufemia/src/extensions/forms/constants/locales/en-GB.ts
index cb609a0fbfa..f11dacd1276 100644
--- a/packages/dnb-eufemia/src/extensions/forms/constants/locales/en-GB.ts
+++ b/packages/dnb-eufemia/src/extensions/forms/constants/locales/en-GB.ts
@@ -120,6 +120,7 @@ export default {
       errorRequired: 'You must enter a national identity number.',
       errorFnr: 'Invalid national identity number.',
       errorDnr: 'Invalid D number.',
+      errorMinimumAgeValidator: 'Must be at least {age} years of age.',
     },
     OrganizationNumber: {
       label: 'Organisation number',
diff --git a/packages/dnb-eufemia/src/extensions/forms/constants/locales/nb-NO.ts b/packages/dnb-eufemia/src/extensions/forms/constants/locales/nb-NO.ts
index 309b6f1266b..e37d5d82b2d 100644
--- a/packages/dnb-eufemia/src/extensions/forms/constants/locales/nb-NO.ts
+++ b/packages/dnb-eufemia/src/extensions/forms/constants/locales/nb-NO.ts
@@ -118,6 +118,7 @@ export default {
       errorRequired: 'Du må fylle inn et fødselsnummer.',
       errorFnr: 'Ugyldig fødselsnummer.',
       errorDnr: 'Ugyldig d-nummer.',
+      errorMinimumAgeValidator: 'Må være minst {age} år.',
     },
     OrganizationNumber: {
       label: 'Organisasjonsnummer',