A response I gave elsewhere in this thread.

This authority will provide you with tokens indicating you are 18+ (or whatever age verfication you may need) These tokens are stored locally, and contain no identifying information other than a simple "is this guy 18+?"

So they're reusable? One token can be used for multiple age checks, right?

If not, then think about what that means.

1. The token gets sent back to the authority for revocation.
2. The token is authorised by the central authority as still valid.
3. The token is uniquely identifiable
4. The central authority knows who it issued each token for
5. The central authority knows who has asked it the verify age.

Sure, the company you're purchasing from may have no new information, but the central authority now has everything it needs to know:

• How often you buy tobacco, alcohol or medications
• What discussion boards you are a member of
• Have you purchased anything age restricted from any store (e.g. propane from a DIY store)