As of 2015, the duration of the validity of a U.S. passport depends on the age of its holder. Those 16 years of age or older at the time of application receive a passport valid for 10 years. For those 15 or younger, the passport remains valid for five years.
Another thing to remember about the validity of your passport is that some countries require it to be valid for three to six months past the travel dates. A traveller should always check the requirements of the country he seeks to visit, as he may need to renew his passport before it actually expires.