As with any law like this, it should apply to systems made for normal end-users with over some minimum number of users. If your hobby Linux distro picks up a million home users then yeah, you're responsible for making it suitable for purpose for as long as you're distributing it. It's the same with accessibility requirements, safety requirements, labor laws, etc.

If California starts knocking on the door of random distros and hobby OSes designed for power users or servers with 2000 average monthly downloads then I'll go to bat defending them.

Though to re-iterate, I'm pretty sure the requirements here are for asking a user to set an age, not to do age verification, so if you did want to comply it would mean adding a Date field to your setup flow and then wiring that up to applications that ask for it.