> 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.

I don't think this belongs on the card to be honest. Otherwide each legislative adjustment would require population-scale updates.

This can go into the reader of anybody who e.g. sells beer to pick your example:

  1. Reader knows beer >= 18 because reader is in Germany  
  
  2. Reader asks card to verify >= 18
  
  3. etc.  
  

Self exclusion would still be possible if there is a standard for it.