A 16-year-old is allowed to work as many hours as he desires, according to the U.S. Department of Labor. There are also no restrictions on the times a 16-year-old is able to work.
Youths ages 14 and 15 can only work non-school hours. They can only work three hours on a school day and 18 hours during a school week. They can work eight hours on a non-school day and 40 hours during a non-school week. Those who are 17 fall under the same rules as teens who are 16. These laws are enforced by the Fair Labor Standards Act, and in some cases can be overridden by state child labor laws. In the event that state labor laws differ from federal laws, the more strict of the two standards is enforced, notes Wikipedia.