>But even then, I can volunteer my ID, keep it permanently attached to a computer running a server that allows certain requests (like the boolean age check), and then provide an API / client that allows anyone anywhere to use it to pass.
That’s not technical problem and it doesn’t have to be a technical solution to it. You will be committing fraud and maybe a few other crimes if underage users are involved. As soon as you will start advertising the service, you will be on law enforcement radar. Or maybe you don’t advertise it, but one of the boys using it will brag at school and get someone’s attention…
You are not entitled to unrestricted access to any online services on condition of anonymity neither it is even possible in real world. 1) There’s always someone who knows and whom you implicitly trust. 2) trusting some random ISP or VPN provider but not IdP or specialized verification proxy is rather irrational.
That’s not technical problem and it doesn’t have to be a technical solution to it. You will be committing fraud and maybe a few other crimes if underage users are involved. As soon as you will start advertising the service, you will be on law enforcement radar. Or maybe you don’t advertise it, but one of the boys using it will brag at school and get someone’s attention…