The militia of the United States shall consist of all able-bodied male citizens of the United States and all other able-bodied males who have or shall have declared their intention to become citizens of the United States, who shall be more than eighteen years of age and, except as hereinafter provided, not more than forty-five years of age, and said militia shall be divided into three classes, the National Guard, the Naval Militia, and the Unorganized Militia. Read More HERE