Side effect: you've now created a child account and will have to wait 18 years for all of the website features to unlock! And don't dare make a second account, or you will get banned for sockpuppeting!
At least one popular mobile game has a policy that the account's birthdate will not be changed under basically any circumstance, and child accounts are severely restricted compared to adult accounts. Parents wanting to take over their kid's account (happens more often than you'd think) end up seriously frustrated with the restrictions.
It validated successfully on 42.
Although maybe that's part of the game?