I came across this and it looks like a non invasive alternative to persona for age verification. According to their website, you scan a passport with your phone, do a liveliness check, then a proof is created that you can use to prove your age. The personal information is processed on your phone, so you don't have to send it, you only have to send the proof.

It also doesn't require any 3rd party service, so it would be free to vrchat. It's also open source.