There exists a baffling contradiction in our society. When a resident turns 18 years old, they are allowed to volunteer for military service, and a forced by law to register with selective services in the case of a draft. We then require that a person must wait until they are 21 years of age to legally purchase alcohol. It is ridiculous that a person can be old enough to die for their country, but not to drink in it.
While the statutes dealing with the legal drinking age are state level laws in all 50 states, the federal government drives this enforcement by withholding 10% of highway funding from states with drinking ages below 21. Eliminating this provision would allow each state to judge for itself what age is appropriate based on evidence, not what garners the most federal funding.