Add validator for min age from a date object

src/components/BirthdayInputField/BirthdayInputField.example.js

@@ -8,6 +8,8 @@ const formName = 'Styleguide.BirthdayInput.Form';
 
 const FormComponent = () => {
   const required = validators.required('A valid date is required');
+  const minAge = 18;
+  const minAgeRequired = validators.ageAtLeast(`Age should be at least ${minAge}`, minAge);
   return (
     <form>
       <BirthdayInputField
@@ -15,7 +17,7 @@ const FormComponent = () => {
         name="birthday"
         label="Date of birth"
         format={null}
-        validate={required}
+        validate={[required, minAgeRequired]}
       />
     </form>
   );

src/util/validators.js

@@ -1,3 +1,4 @@
+import moment from 'moment';
 import { types } from 'sharetribe-sdk';
 
 const { LatLng } = types;
@@ -68,3 +69,10 @@ export const emailFormatValid = message =>
   value => {
     return value && EMAIL_RE.test(value) ? VALID : message;
   };
+
+export const ageAtLeast = (message, minYears) =>
+  value => {
+    const now = moment();
+    const ageInYears = now.diff(moment(value), 'years', true);
+    return value && value instanceof Date && ageInYears >= minYears ? VALID : message;
+  };