Such a weird thing to get upset about. This is an easy way to allow flagging a user as underage without exposing actual identification to the users. You don’t have to put in their actual birth date, just use Jan 1 of whatever year.
If this sort of thing is accepted, this lets websites and games do a simple check and then all blame for underage access is on whoever setup the account on the computer.
Do people honestly prefer websites blocking access to countries and states because they have no way to check a users age? Those websites don’t give a shit, they just don’t want to be responsible. This gives them that out.