> Crypto where the OS (or a website) can ask the card: "Is the holder of that card over X years old y/n?" and the card would just answer with a binary yes no question without exposing any other data while still checking the government signature.

This is the same as "What's the card holders age" by simply binary searching for it. A better way would be:

1. Have the card define the countries age access levels. (Example in Germany: >=16 [Beer/Wine], >=18 everything else) 2. The app can only ask: "Is [BEER] allowed for the card holder y/n?

This makes it immediately cross-legislative and protects the exposed data from meta analysis.

Edit: This would allow for self exclusion too. Make it possible for individuals to give up access to gambling/alcohol/tabacco/porn nationally.

in the Netherlands we have a better system called iDIN; it works like doing an online payment (iDeal / WERO):

* Website asks for age verification * User is redirected to their bank * Bank asks the user to log in - username/password, 2fa, bank app (whose login is behind the device's security and a secondary verification like PIN code or biometrics) * Bank tells the requester that the user is 18+, no more

This leverages a trusted party (your bank, which is subject to heavy IT security regulation and audits) and you need to show ID to open an account anyway), secrets only you know (and your kids can't easily take), phone security systems, etc. Does not require uploading ID to a 3rd party, does not require changing how IDs work, etc.