What makes you think it will stop there? Once the groundwork has been laid for this framework, all they need to do is roll out v2 which requires a little more from the user, etc.

Most servers won’t check this bit at first because they don’t need to or care, but once the technology is in place, it won’t be long before legislation mandating the checking of that bit begins to roll out affecting industries and providers that deal in topics and goods deemed to be bad for the children (it won’t stop at porn).

Once that happens, minors will learn ways around the check (or parents will be lazy and give their kids access to adult logins, etc), and the “need” to enact stronger checks will be pushed for and…

Put all of it together and you’re heading towards an Internet without anonymity in a couple of decades.

Any sort of hardware attestation that non-trivially identifies a person to verify their age is going to be used to track and exploit people.

Anything less than that isn’t going to be effective for the supposed purpose.

The moment we need photo ID or government issued keys to access computer systems, things will get a lot more ugly real fast.