I think with alcohol, look at how drinking in Europe is handled. In some countries over there, wine is consumed by underage folks all the time.
Even though it's with their meals for the most part. Therefore removing any stigma which could otherwise be attached to the drinking. Basically it's just part of their meals all the time.
In the US, underage folks are constantly bombarded with messages about how they can't drink until they're 21 and even though many do so anyway, they feel like they're sneaking around. So, they tend to go overboard and by the time they reach legal age, the damage psychologically has already been done. Not only is the age thing a black and white deal, you're either legal or you're not. But, like another poster pointed out, so becomes the drinking. Not to go off on a drug use tangent but drug use in the States is sort of in the same ballpark. Curious what others think on the topic.