Federal Laws

The U.S. Department of Labor sets the Federal rules for jobs including minors, those under 18. Basically 14 is the minimum age for employment.  If you're under 16 the Government limits the number of hours you can work.  Rules vary depending on the kind of work and job you want.  Below is the Department's Website, a great source of information:
http://www.dol.gov/dol/topic/youthlabor/agerequirements.htm.