J. Christian Adams, over at PJMedia examines the federally mandated drinking age and argues that it should be lowered to age 18. He has a good discussion of the issue, and I agree that it deserves a second look.
I have long held that we should have one age of majority. If, at some point, the state decides that a person is competent to enter into contracts, buy and sell property, enter into marriage, obtain the right to vote, and serve our military, then that person should also have the right to walk into a bar and buy a beer. It's a simple concept. Either you're an adult or you're not.
Other arguments can be made that the states are more properly the custodian of the question, that it is simply not the province of the federal government to decide such issues.
Interestingly, one of our local municipalities is this weekend, deciding a local ballot measure that would change the city from basically dry to basically wet. There are five options on the ballot that voters will address, basically from a strict prohibition, through low-alcohol package sales to high-alcohol package sales, to drinking in restaurants, to wide-open bars. Historically, this town has been "dry", but enough citizens got together a petition that the city was required to put it on a ballot.
These are interesting questions, indeed. Let freedom ring.