Comment by mr_mitm

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...