If we are aloud to serve in the military think of the things that person will be going through if he/she comes back. It would be easier on that person and the police. If the drinking age will not be lowered to the age we can enlist then one of those age requirements isn't right.
If the legal age of adulthood is 18 and people are allowed to serve in, and required to enlist in, the military at 18, the drinking age should match that. This would save money tracking down some underage drinkers and servers and make things much easier to police in bars and places that serve/sell alcohol.
A person who is 18 years of age is allowed to serve in the military and possible give their own life in a war zone. Makes no sense then that someone of that same age is not allowed to consume alcohol. It poses no national security risk, no more than enlisting within the military.