None of this is necessary. First, the only devices that actually need to be gated are cell phones.

The user agent should simply send the user’s age of the parental lock is set up and the websites required to respect this.

Parental controls and the OS should be robust enough to not let kids bypass it (e.g.: by installing a browser that skips the header, or blocking proxy websites)

Done.

Cellphones only because those are the devices kids can have on them all the time and can easily use in private unsupervised.

They want it to equal identity verification! When virtually every top tech executive who wants a favor is at the inauguration and you have companies doing 180 degrees on support for something they previously furiously opposed, someone is getting something they wanted. It seems naive to think otherwise. Furthermore, the current administration in the U.S. fired or ignored the competent people to which you’re referring, and those people oppose a centralized repository of various metadata because it creates a central point of failure, otherwise known as a target, that is generally a bad idea for both our nation and our citizens. Of course there are agencies in the federal government that possess this information already, but they possess it for their purposes only. This is good because it means that it’s both more difficult to abuse internally in addition to being more cumbersome to collect externally.

It's a political problem, not a technical problem.

Yeah this is a basic problem that's been solved since the advent of PGP. As many other posters have said, this isn't about age verification.

There's still a whole DB matching IDs to keys waiting to be leaked. The US government can't even keep it's own personnel records safe and you think this won't get stolen and used to target people?

This still criminalizes sharing "adult" information with people who are not on the government's approved list (the things states do to crush dissent are not safe for children.)

why would any site on the internet need to give a damn about is_citizen? That's just gross to me at the mere suggestion. If it's a government service site, then they already know that information. If you're trying to use something like social media, then it couldn't possibly matter less.