This has been widely discussed, and initial implementations exist: the EU digital wallets are doing exactly this. https://ec.europa.eu/digital-building-blocks/sites/spaces/EU....

In theory, every EU state will have to support this soon so users can use it to verify age privately online. Still work to do to roll this out for real, but the technological part is very much already happening and I think the rollout plan is committed.

No. You seem to not understand how government works. It will never be anonymized so it's an awful idea, you basically suggest to link accounts to a passport.

The german gov id supports that. They have a PKI and the id is a smart card with a cert and private key on it [0]. It lets you answer the question "are you over 18" with a zero knowledge proof. I guess it only proves you have in your possession a valid id AND know the PIN to it, but that should be fine. France apparently has this, too, according to the article.

[0] https://www.personalausweisportal.de/Webs/PA/EN/government/t..., https://www.bsi.bund.de/EN/Themen/Oeffentliche-Verwaltung/El...

> Both the request and the response can be appropriately anonymized so that the government doesn't know the site, and the site doesn't know the person's identity.

Yes that's how it's done in France for instance, and generally how it's being discussed in the EU.

Exactly. Governments that really care about age verification should provide the tools to do so. They have the means to do so without violating privacy. Something like the Dutch DigiD service (the one they're about to sell to the US despite literally everybody opposing that) would be a great basis for this; just add an age verification service to it. They already know who you are in the most legal sense possible.

> There should be a standardized government ID service/API

Most European country already have one, some are still testing theirs. They're required by the EU to make one accessible to their citizens by the end of this year, in the context of the eID project [0].

[0] https://commission.europa.eu/topics/digital-economy-and-soci...

> if the government ID service has appropriate 2FA and security.

You're kidding right?