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.
The U.S. Army accepts enlistees who are 17 to 35 years old. In most cases, you must be in your senior year of high school or have graduated from high school to join. The Army accepts people who have passed the general educational development (GED) test.