The cutoff age to join the military differs in each branch. As of January 2015, it is 34 for the Army and Navy. It is 29 for the Marines, 39 for the Coast Guard and 27 for the Air Force. The limits may change based on prior or reserve service.
People must be at least 17 years old to join any branch of the military. Other requirements include being a United States citizen or resident alien, passing a physical exam, and having a high school diploma or an equivalent. Each branch of the military also has its own further requirements.