https://news.ycombinator.com/item?id=46223051 This one works well. Or at least, as well as age verification for tobacco and alcohol. And equally privacy-preserving.

Agreed! Great idea. I'll save others the click:

"The insistence on perfect age verification requires ending anonymity. Age verification to the level of buying cigarettes or booze does not. Flash a driver's license at a liquor store to buy a single-use token, good for one year, and access your favorite social media trash. Anonymity is maintained, and most kids are locked out. In the same way that kids occasionally obtain cigs or beer despite safeguards, sometimes they may get their hands on a code. Prosecute anyone who knowingly sells or gives one to a minor."