John McCardell (a president emeritus and a professor of history at Middlebury College) in the Atlantic argues that the US national drinking age of 21 is a failure -- it has failed to stop underage drinking, and has instead driven it underground and made it more dangerous. I grew up with Ontario's drinking age of 19, but I started drinking at parties and so on at about 14 or 15, often to bad result; ironically, once I was old enough to drink in bars, I drank a lot less, as the culture in bars was generally different from the parties I'd drunk at until then.
The way our society addresses this problem has been about as effective as a parachute that opens on the second bounce. Clearly, state laws mandating a minimum drinking age of 21 haven't eliminated drinking by young adults--they've simply driven it underground, where life and health are at greater risk. Merely adjusting the legal age up or down doesn't work--we've tried that already and failed. But federal law has stifled the ability to conceive of more creative solutions in the only place where the Constitution says such debate should happen--in the state house--because any state that sets its drinking age lower than 21 forfeits 10 percent of its federal highway funds. This is called an "incentive."
So what might states, freed from this federal penalty, do differently? They might license 18-year-olds--adults in the eyes of the law--to drink, provided they've completed high school, attended an alcohol-education course (that consists of more than temperance lectures and scare tactics), and kept a clean record.