Okay - so you verify age and what else?
What combination of details can you validate on that is meaningfully privacy-preserving and couldn't result in wide-spread re-use of tokens?
Additionally - what would prevent some kids from getting a homeless man in the city to hand them his ID, get a facial scan, and everything else you can think of to generate a token and then pass that token around?
ZKP are a cryptography-nerd's joy but are are categorically unsuitable for the purpose of age verification. I stand by this without the slightest reservation.
the same thing that prevents them from doing reuse right now: platform detection mechanisms. the difference is that right now the identity of the subject is known whereas with ZKP (nullifier approach) only the dirty token is known and where that token was used.