Webform validate 18 years old (GNU Date Input Format)

Question

I'm looking for a valid webform date pattern, to validate a user's birthday (component date).

I want to make sure the person is 18 years of age or older. However, Drupal requires the GNU Date Input Format.

This seems not to work - Drupal shows no error message at all ?

There is also a related answer Field Validation: 18 Years or Older, but this seems to be super complicated and does not affect the webform module.

Answer 1

Here's the solution for this annoying "feature":