The length of validity for U.S. passports depends on the age of the passport holder when the passport was obtained and the type of passport issued.
If a passport is obtained for someone younger than 15, it is only valid for five years.
An adult passport is valid for 10 years from the date of issue.
Some countries do not allow entry into the country if the passport is due to expire in six months or less. Obtain a new passport before travel.