[ghm2199]

What I don't understand is why not have designated actors/ombudsman like notaries in the society that can verify your age/id without anyone knowing what it's for.

One can easily implement a nationwide system like this. You can trust people in your own community. There are no central govt actors. In such a system no one has any knowledge of which service you are proving your identity/age for and the cryptographic approval can be done without any ids being exchanged. The input to the ombudsman is a hash you provide which he can sign with his key and send to a server, that can ask the ombudsman: "this thing you are signing is for age verification > 18, check persons ID and press confirm if that's the case". The ombudsman presses confirm after checking the id and you are done. Every city municipality can elect a local councilman/notaries to do this, for a small fees.

[zigman1]

Eu actually plans to introduce something similar through its EUDIW initiative. It will be a digital wallet focusing on privacy preservance and user control over attributes that are shared.

It will take some time tho before it is successfully implemented.