Children can take the class at 12 years old, and receive their certificate at age 13. 
Kids 13 and up can take the course and receive their boat safety certificate.

There are two minimum ages:

13 years old for vessels powered by electric trolling motors, or vessels 12' or longer with less than 10 total HP.

16 years old to operate of all other power vessels, including personal watercraft, this includes out-of-state residents.