I didn't really get the panic on the systemd PR. It's literally just adding a "birthDate" field to the user record that behaves like any other field? If you're running your own system you can change your birthdate to whatever you want since you have access to sudo.
Maybe kinda make sense for people who want to give their kids accounts and have their access locked down? It's not like it's any different than those "enter your age" screens on Steam or whatever.
Also:

We're about to see millions of 126 year old Linux users lmao