You live in NJ, so things operate a little differently. Basicly, in order to work on an ambulance, the minimum level of training (certification) is Emergency Medical Technician-Basic, an ~130 hour course, followed often by state/NREMT practical and written exams. From there, you should get your card, and be set to work on the road.
Elsewhere in the country, the minimum age to attain EMT-B is 18 (also the legal age of majority), but NJ and CT operate slightly differently, offering the cert to students as young as 16. In NJ, particularly, your training may be paid by the state first aid (grade) council, but only if coordinated by your local township first aid squad. Get in touch with them for more info.
There is much discussion (which you may see here), about the role of a class as short as EMT-B, and whether anyone under 18, or even 21 should be working on an ambulance. Here is what I can tell you: If you are interested in EMS, get in touch with your town's ambulance service, but enoy your high school years. Hang out with friends, party, "Make Mistakes, Get Messy".
Good Luck,
Dan