I think it should be un-banned unless there are certain individuals that are abusing it. It should only be banned for people that abuse it.
I would like to make it clear that civil law does not ban alcohol to people under age if it is for religious reasons. You could say that any kosher wine is for religious reasons. Even if it is not for kiddush, drinkling at a simcha can count as a religious reason according to me.
Well, perhaps they should lower the age for drinking alcohol at home with parent's permission.
Now, I don't think that wine for simcha can be considered a religious reason. It's not a mandatory mitzva in Judaism, with the possible exception of Purim. Jews are required to enjoy any non-sinfull thing they like during Shabat. So, we should unban everything Torah allows to do with moderation, and Gentiles who don't follow Torah will abuse it.
Now, for practical reasons, we must see if a law is being fulfilled, and what is the fate of those who break it. If a teen who illegally takes alcohol, is just fined, and can keep a normal life, then better keep it banned. Some teens are eager to break the law just to be rebels. Then better have a lees harmfull thing banned, so that in case they purposedly wish to break the law, they don't turn to something worse.
But if the offender is persecuted, treated as a crimnal, and rejected by society, just of that offense, then better unban it, lest he seeks the companion of other offenders and criminals and gets ruined.
BTW, here in Argentina it's forbidden to sell cigarettes to under aged, but no law against them smoking. They can esasily send an adult to buy it, and it's no offense. I think the Govt. should ban it. How is it in USA?