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)
Across the United States Armed Forces, the maximum age for enlistment for someone who has never served in the military before depends on the branch. For the Army, the maximum age is 35. For the Navy, age waivers start at 34-years-old. For the Air Force, the maximum age allowed to join is 39-years-old. The Marines have the lowest maximum age for regular military service at 28-years-old.