ARTICLE II, SECTION I of the United States Constitution states that a person seeking the office of President must:
Be at least 35 years old
Be a natural-born citizen
Have lived in the U.S. for at least 14 years
The 22nd Amendment, adopted in 1951, prevents anyone from holding the office for more than two terms or one term if he or she held the office for more than two years but was not elected.
Read some fun facts about our 43, I mean 42, presidents from Infoplease.