There a various attestation methods that have been used over the years. For example, some states have (or at least used to have) a drivers license that is in p

There a various attestation methods that have been used over the years. For example, some states have (or at least used to have) a drivers license that is in portrait orientation if you are under 21 and landscape orientation if you are older. A store clerk only needs to look at the photo to make sure it matches the holder and knows whether that person can buy beer or not. A digital identity system could offer various attestations that reveal nothing about the user except that they are above a certain age or whatever else you care about. Login.gov could offer this as a service.