Ideally you also don't need to verify it more than once, though. Otherwise, it will be friction that detracts from the user experience.

Please elaborate what is “fun” about that fact? The drinking age is 19 in most of Canada, 18 is the exception. And the drinking age varies all over the world.

It used to be between 21 in most of the US until the voting age was lowered to 18 in 1971. It was then either 18 or 19 in most states (generally the more liberal ones) until 1984 when the national minimum was passed. 19 really is sort of a sweet spot for socially liberal North America.