I have had these thoughts:
California Prop 12 regulates pork and egg production (crafted by “animal rights” groups with the objective of making both prohibitively expensive). This got contested all the way upstairs, and the Supreme Court found that under States’ Rights, if California (CA) wants to be lunatics, they are allowed to be lunatics, and upheld it. HOWEVER, the court also found that under the Commerce Clause, CA law did not apply outside of CA, and that CA could not demand egg and pork producers in other states to be equally loony before they could sell product into CA. In short, CA cannot in any way enforce this outside their own borders, not even by restricting commerce from other states.
So that’s where it stands, under court precedent: California and Colorado can do this within their own borders, but they can’t enforce it on any other state, nor can they prohibit the noncompliant from crossing state lines. (Same as they can’t stop vehicles driving in from other states.)
And under the above, an OS preinstalled in another state then that PC sold into CA would not be regulated, as doing so would violate the Commerce Clause.
Enforcing it at all is a different matter, since the internet knows no such boundaries, and geofencing won’t prevent someone from using a VPN, or driving to Las Vegas and downloading eg. Fedora anyway (or just using an older OS, so long as they don’t need to use “software stores”). And there’s folks like me – I’m on satellite internet, and it geolocates me in another state entirely, about 800 miles away.
And exactly how do they plan to get users to comply? The only way to do so is if OS vendors enforce it. Fill in the age field, or it won’t install. After that, you’re into the murky grey area that surrounds software piracy, because absent identity verification (NOT required under this CA law’s text) you can’t stop users from inputting any age they like. One suspects were such ID verification enforced, it would work about as well as those states’ voter verification (ie. not at all).
What this DOES do is give the nefarious legal protection: “Your kid claimed he was 21, so it’s not our fault if he did $_age-restricted-by-law-thing on our site.”
Microsoft is the 800 pound gorilla here, and what Microsoft does is going to dictate whether this flies for everyone else. If they go along with it, anyone who doesn’t is functionally dead in the market, and such laws will spread elsewhere. If Microsoft says “you-and-which-army plan to enforce this?” then the law is DOA instead.
However, I fear Microsoft will say “Nifty opportunity to enforce that Microsoft login” and go right along with it. (Especially as I believe the next major iteration of Windows will be OS-by-subscription, which will require a credit card or bank account for billing. What did you think TPM was really about, hmmm?)
And yes, if parents hadn’t offloaded so much responsibility for parenting onto the government (albeit strongly “encouraged” to do so by mandatory public schooling) we wouldn’t be having this discussion, but that horse is long since out of the barn, down the road, and out of sight.