According to the U.S. Department of State, passports for Americans who are at least 16 years old when the passport was issued are valid for 10 years. Passports for those who are 15 and younger are valid for five years.
It is important to check the issue date of a passport to determine how long it is valid. The issue date is printed on the data page of a passport book or on the front of a passport card. The passport should be renewed at least nine months before the expiration date. Some airlines prohibit passengers from boarding if their passports are valid for less than six months beyond the travel dates.