What if I could purchase a unique QR code, good for maybe a month, that I could use online to prove my age?
There'd still be problems in the US with 1st amendment issues, but I'd at least remain anonymous.
This is just moving personal data responsibilities from service providers (e.g. porn sites) to the central authority (QR code maker and verifier). Unless there is a semi-anonymous way of purchasing age proofs, e.g. over the counter.