I think that the major current closed-source OSes today are busily harvesting all the data they can anyway, and the vendors probably don't care much about also grabbing age, but stuff like, oh...is it illegal under this law to distribute proprietary versions of older OSes now? Like, classic MacOS, say. That's definitely not open-source. And Apple is not going to go back and do a new release of classic MacOS to add age verification to it. But...there's still some old software that you need classic MacOS to run. So...is it illegal to distribute essential software required to run classic MacOS software in California as of the middle of next year?
I mean, you might be infringing on copyright as well, but Apple may be okay with people copying classic MacOS around, as they can't really make any money off it today. But this is the State of California, not Apple, that would act here.