Some day, many years ago, some guy left some oddly gathered ingredients in a container and forgot about it. A week later, a buddy of his bet him two wives and a scrawny goat to drink the stuff. After he did, he said it wasn't bad, his inhibitions were lowered, then he threw up and passed out. The craze spread and alcohol is now completely ingrained in almost every culture of the world.
I think 18 should be the legal age for everything; a matter of treating people like an adult. Its not like anyone actually grows to maturity before, say, 25-30ish, so you're not saving yourself much trouble by limiting 19 year olds from purchasing alcohol.
I'd prefer obscene tax rates, and some experimental ingredients that would make people who consume to much bald, impotent, fat, and ugly.
Oh, wait, that already happens? Well damnit, what is it about the stuff that is so appealing?