For what I understand, OpenBSD could just patch useradd so that the age category is mentionned in the comment field of /etc/passwd or a random text file in /etc.

Haiku could just run an automatic dialog asking you if you are minor, in Illinois or California and write a text file with the corresponding age category of said person.

These bills do not mandate that the user cannot modify that information AFAIK.

I can't imagine OpenBSD would be bothered by laws specific to a very small selection of US states.

By adding a simple birthdate field to your account info and a system API of some sort for retrieving the account owner's age range, same as everyone else.

Tbh they probably don't care about anyone other than Microsoft or Apple, though it's certainly not written that way.

OpenBSD devs have signaled noncompliance from their Canadian fortress of freedom.