> In the US at least, the 21 yo drinking age is mostly a wholly pragmatic law [EDIT: laws. It's state by state but there was a big federal stick attached to highway funding.] to reduce teenage drunk driving (which affects more than the individual).
To add another voice of dissent to the Danish poster's point of view, in Australia, you can drink at any age with parental consent (though child abuse laws would come into play if you do anything ridiculous) and you start to get your license at around 16 depending on the state.
Also, getting a full license in my state is a much involved process. It takes around 5 years if you aim to get it as young as possible: 1 year of supervised driving with a fully licensed passenger (there must be 120 hours of driving until you move to the next stage), then 1 year of a limited probationary license ("red P's") and finally 3 years of a less limited probationary license ("green P's").
Throughout this entire process, you cannot have _any_ alcohol in your blood while driving.
I think this, plus public awareness of drunk driving, is much better than just restricting drinking until you're 21. It means that usually, before you even get behind the wheel, you've had years to experience the effects of alcohol and get the thrill of it out of your system. Then once you're driving, you get used to the idea that you can't even have "just a little bit".