There are places with a policy of asking everyone for ID -- I know because they're the only places where I've been asked for ID. Of course, for both the knife

There are places with a policy of asking everyone for ID -- I know because they're the only places where I've been asked for ID. Of course, for both the knife and the alcohol regulations, the law is around age. ID is merely the mechanism that everyone uses to validate age, as it's settled practice that doing so will prove the ID card holder's age sufficiently for the purpose of the legislation.