Earlier quoted context omitted.
That sounds nightmarish. I don't want the verifier to know what porn sites I visit. Someone else proposed the following system to me: a third party authority issues a certificate which I can then use to prove I'm 18. The CA cannot see where I use the certificate, though.
Er... The CA needs to be used to verify the certificate by the third party, ergo it will know the websites. It's virtually impossible to make a verification system that's anonymous. Somewhere the third party and authenticator will need to share a secret that you cannot touch. Furthermore, you would need the government to agree to this system and mandate this system universally and pay for the authentication services…
The problem is that my ID contains too much information; I would prefer a document (i.e. digital certificate) that only certifies my age, not my name, address etc.