In 1920, the Supreme Court applied the Supremacy Clause to international treaties, holding in the case of Missouri v. Holland, 252 U.S. 416, that the Federal government's ability to make treaties is supreme over any state concerns that such treaties might abrogate states' rights arising under the Tenth Amendment.
Age. To join the Military, you have to be at least 18 years old (17 with parental consent). As for the upper age limit, it depends on the Service and the program: Health Professions Scholarship Program (HPSP): 36 (for the Navy, you can be no older than 42 at the time you enter Active Duty, following your degree completionâunless you were granted an age waiver when you were recruited)
Coast Guard Reserves - Age 39. In most cases, the amount of age that can be waived depends upon the amount of time the individual previously spent in the military. For example, let's say that an individual has four years of credible military service in the Marine Corps and wants to join the Air Force. The Air Force could waive the individual's maximum enlistment age to age 31 (Maximum age of 27 for the Air Force, plus four years credible service in the Marines).