Just FYI, a handful of states have 19 or 21 as the age to buy tobacco, and while I think you're right about the age to gamble being 18 in most states, most casinos require you to be 21 – at least from my anecdotal experience.

This doesn't change your overall point about fake IDs, but it does support the idea that America has a bizarre set of age limits around "sinful" behaviors.