The President is both the head of state and head of government of the United States of America, and Commander-in-Chief of the armed forces. Under Article II of the Constitution, the President is responsible for the execution and enforcement of the laws created by Congress.
You can join some branches of the United States military at the age of 38 years but not others. The Army, Navy, Air Force, Marine Corps and Coast Guard each has its own minimum and maximum age requirements for enlistees, including for new recruits in the active-duty ranks, the Reserves and the National Guard.
Applicants who are 17 years old must have the consent of a parent or legal guardian before entering the military. Age limits for entering active-duty service are as follows: In the Army, the maximum age is 34. In the Navy, the maximum age is 34. In the Marine Corps, the maximum age is 29. In the Air Force, the maximum age is 39.