This is not a coincidence. When states lowered their drinking age in the 1970s, they got more drunk-driving deaths among teenagers than similar states that stayed at 21. A 1983 study in the Journal of Legal Studies concluded that any state that "raises its drinking age can expect the nighttime fatal crashes of drivers of the affected age groups to drop by about 28 percent."
There are other arguments for lowering the age. Maybe the most popular is that if you're old enough to join the Army and die for your country, you're old enough to buy a beer. But there is a good reason to avoid such blind consistency. Among the qualities that make 18-year-olds such good soldiers are their fearlessness and sense of immortality -- traits that do not mix well with alcohol.
Besides, we don't have a single age threshold for adulthood. We give driver's licenses to 16-year-olds, but a 20-year-old Marine returning from Iraq will find he may not buy a handgun or gamble in a casino.
Why permit 18-year-olds to vote but not drink? Because they have not shown a disproportionate tendency to abuse the franchise, to the peril of innocent bystanders.
Another reason is that extending the vote to 18-year-olds doesn't let even younger people gain illicit access to the polls. But if high-school seniors could legally patronize a liquor store, sophomores would find it much easier to get party fuel. Raising the drinking age to 21 reduced alcohol-related traffic fatalities not only among 18-year-olds, who lost the right to drink, but 16-year-olds, who never had it.
It's not hard to make a logical case for allowing 18-year-olds to buy alcohol, but only if you disregard the practical effects of letting them do something that many of them are not mature enough to handle. In this debate, the ultimate wisdom comes from Supreme Court Justice Oliver Wendell Holmes, who reminded us that sometimes, a page of history is worth a volume of logic.