Advice... go to college (preferably one with an EMS program), get you basics such as algebra, psych, anatomy I & II, Physiology, English composition and literature. Meanwhile, talk to your college counselor, they might get in touch with a EMS advisor whom can allow you to do ride along. After talking into detail of the good and the bad.. then after this is done, apply to a EMT course. You will find Basic EMT class a breeze after completing some general science classes.
The reason is multiple, At the age 18; most services will not hire you due to the required age level for insurance companies. After your exposure to EMS & detailed interviews about EMS, I suggest going straight through from EMT to Medic. That is if you want to have decent pay and a job. Many might suggest working as an EMT for years, and that is nice, but it is too difficult to find EMT jobs. As well when you are completed as a medic, you will be treating patients in more in-depth, have a job/position, higher seniority, and much higher pay and job security.
If you do not so happen to like EMS, then nothing is lost... you will have some education for another career.
Good luck in your career!
R/r 911