> There are various other potential methods to verify one's age, all of which are forbidden by OFCOM. Account age, zero-knowledge proofs, key signing, some kind of OAuth thing, physical tokens that require proof of age to buy, etc. The only permitted ones require your to link your real-life identity.

This is just not true. See 4.17 here, for example [1]

[1] https://www.ofcom.org.uk/siteassets/resources/documents/cons...