It varies from state to state. Usually the minimum age to enroll in class is 16. However, many facilities mandate that you be at least 18 to work there. You can find out for sure by contacting your state's board of nursing. You will find the links at the bottom of this page. Good luck!
It would probably depend on your state laws . Where I live minors can work at 14 with a workers permit. I dont recall my cna class having an age requirement. I started the class at 16 and started working as a Cna at 17