How would age verification even work here? Would it work?

Depends on the exact wording of the law, but an attempt can be made. It would be a horrible waste of everyone’s time as well as require significant time investment from instance admins though.

The whole concept is idiotic, especially since even the most complex age verification schemes can be bypassed by using an adult to verify on behalf of a child (and most can even be bypassed with video game screenshots). You end up with the same system, functionally a checkbox asking if you’re old enough, but with all the added invasiveness and potential risk.