alt Hacker NewsThat's because you're treating AV as a system that must be 100% correct immediately. This isn't banking or an election.
As soon as you loosen off the requirements to "reasonable effort", you can start looking at account age, facial features, social attestation, and include retrospective tools to revisit someone's verification if they get in and start acting like a child. Heuristically messy but far from impossible to demand a stronger form of verification if their original might have been borderline.
The goal is broad coverage, not complete. Screening doesn't have to get 100% to have an effect.
I understand it doesn't need to be 100% correct. But I think what you're describing is either (A) going to be very privacy invasive, (B) going to create problems for lots of adults, or (C) going to be precisely as effective as a checkbox saying "I agree I am over 18 years old".