> Porn sites and already doing this.

I think a better example might be places like polymarket (not allowed to operate in us) or usatoday (serves an EU only version with no cookies). The technical limitations on those systems are both GeoIP as far as I'm aware, and that seem sufficient for regulators.

What I find more interesting is that what you want is within the scope of this law. It's only required that the operating system takes in your age from an admin, from there the application (user agent/webbrowser) is supposed to handle the blocking, which it could do with a header as you suggest.

I will note that you are going to find a lot of libertarians that would oppose banning GeoIP circumvention.

Are small children losing money on gambling sites already? If so I have not been paying attention. That really needs to be reigned in as they are likely using their parents credit cards without their permission. We need to break that habit before they reach the age of consent and that becomes a punishable crime. Our prison system already has too many young people. That's an awful way to start.