Meta is being intentionnaly dumb

> a public service that delivers "I am in the xxxx age bracket" time-limited (month ?) attestations

Doesn't have to be a public service. Your bank/local council/insurance company/employer can all attest your age bracket. An app on your phone that scans your passport/ID card can do it. All you need is a standard mechanism to trigger them.

The issue is more that in the US people desperately hold onto the idea that they can be totally anonymous to everyone, including the government, while ignoring that businesses and the government amass your personal data in a non-transparent way. Which mean your birth date and other personal data is already spread around, but you can't actually derive any benefits from it. Worst of both worlds.

Better to have a structured system where you can view and verify what data people have about you, and then be able to use that for your benefit. Like the aforementioned attestations.