I'm a middle-aged Navy veteran. I'm not Vietnam old, I'm 43, 1st Gulf War old. There's been no draft in my lifetime- but ...
The "equal protection clause" in the 14th Amendment - which was one of the deciding factors in the Wednesday Supreme Court ruling that (fortunately) defanged DOMA and will allow many of my friends to legally marry the people they love - it also applies to other people, including college students, and the "legal" drinking age.
"... nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws. "
Currently, there is not a national legal drinking age. It is theoretically left up to each state. However, the U.S. Department of Transportation will not provide any matching highway funds (sometimes 50% or more) to any state with a drinking age lower than 21. Hmmm.
As far as I'm concerned, a citizen is a citizen. While there are (and should be) special protections for children and even limited citizenship rights for minors... once there is an age of majority- where a person can be drafted, sued, found criminally guilty and even vote... that person is of the age of the majority. That person shall not have lesser rights, as restricted by the states, than any other citizen of majority age.
How has this not yet been challenged? If the federal and state governments want to prevent people under the age of 21 from drinking (and statistics certainly point to a reason for this), then they should also prevent those same under-21 persons from voting, serving in the military, getting married or being sued. Using that mistaken theory - If they aren't "adult enough" to handle drinking, then they shouldn't be relied upon to be our nation's fighting men and women.
There should be a singular age of majority/citizenship in the U.S. When is somebody a "full citizen?" When there are aged 18 or 21 or something in between? Make a decision.
If somebody is old enough to fight, bleed and die for our country, old enough to vote, old enough to enter into comparably trivial contracts, etc... they are old enough to fucking drink a beer or 10.