I am currently in the military (Army) and have been flying fixed and rotary wing for the past 10 years. The Army will let 18 year olds fly depending on when their birthday falls after high school graduation. We in the Army call it "high school to flight school." I will say this, however, by the time a recent high school graduate finishes with Warrant Officer School they are approaching 19 and by the time they finish the flight program they are approaching 20. Long story short, the Army does let really young people into the flight program.