Greetings!
One has to wonder with all of the underage drinking that occurs in the U.S. whether the 21 year old minimum drinking age makes any sense at all. It certainly has not deterred underage drinking. By the way, although teenage drinking and driving is a serious problem, I would venture to say that most drunk drivers are OVER 21, thus another reason to question the effectiveness of the law.
IN my opinion, I do not think that underage drinking inside a private home or in an enclosed yard, or the drinking of wine or beer in a restaurant setting by a minor who is with their PARENT(s) or legal guardian should be illegal at any age. In all of these situations, the parent (or guardian) should be responsible for both introducing and educating the child about alchohol and for supervising their children's consumption as they see fit.
I think that alcohol should not be sold to a minor under age 18 so minors would have to acquire their alchohol from an adult or out of their own home, again placing the responsiblity upon the parent or guardian (adults) where it belongs. Of course any actual public drunkeness, including drinking in public by a minor should receive a stiff penalty. Operating a car or machinery under the influence is already a crime with severe penalties for persons of every age so there is no change there, except maybe to make the penalties even more severe.
-Eduardo