ceejayoz> You want to let every merchant I swipe my card at know my age? To improve privacy?
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SG> Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize.
The obvious solution is instead of "every transaction comes with the user's birthday", the vendor can in some way set a minimum age enum of say (13, 15, 18, 21, 25) — a handful of ages that are significant with respect to some law or regulation. Then the transaction succeeds or fails.