Drinking at 21?

How did the age of 21 come about as the "legal drinking age" in the United States? I ask that question somewhat rhetorically, because I really don't want the answer, because that would probably ruin my forthcoming diatribe!

I think 21 was arbitrarily chosen, and I think that the age should either be lowered to 18, or raised to 25! I think this, in part, because these numbers two are simply arbitrary, yet can be associated with a variety of other lifetime milestones. Even though I'm far past the age of 18, I've always wondered WHY 21 was set aside as the "magical legal drinking age"? At 18, you can legally marry, enter contracts, and sign your life away to either of the military branches of this country, so why then, if given THIS MUCH RESPONSIBILITY is the age to legally imbibe in alcohol consumption still held off until 21? It's not as if that age restriction somehow magically keeps kids AWAY from alcohol. It just seems arbitrary and ridiculous to me!

Everyone's so enthused about "young people and their participation in this year's election", but what would happen if those young people decided to turn their attention towards this issue?

It just seems crazy to me that you can enter contracts that can change your life, open credit that can potentially ruin your financial life (for decades), and make the ultimate decision to put your life on the line for this country and its ideals, but can't get a drink until 3 more years have passed.

This sucks! And who gave MADD (Mothers Against Drunk Driving) the power to enforce such an age limit arbitrarily?