Let's just add it to systemd

Meh, adding an age question to adduser wouldn't be that bad, we could even replace the current room number question

And non-commercial distros?

that's great. hey, why don't you ask the UK how fining foreign entities millions of dollars for not doing age verification is working out for them.

you see, laws only apply if the state has the ability to enforce them using violence. california does not have that ability outside of california. california can chew the bark off my big fat log for all I give a shit about the laws there.