Make this solution whilst I was learning regex. Forked improved solution to this solution.

Nice exercise, but the tests don't cover all possible "corner cases". As a result some solutions that don't follow the description are accepted.
Things the tests don't check:

• String with 2-digits Years should be accepted
• Strings where the Month or the Day is '00' should be rejected
• Strings where the last 4 characters contain something different from numbers should be rejected

this will accept "00" as a valid month or as a valid day.