im newly 20 myself and had the most difficult time finding an EMS company both willing to hire me with an insurance agency willing to cover me. I got my Basic EMT three days after my 18th birthday... was forced to wait in fact to sit for registry until that time. im not sure where you hail from, but so far as im aware, dont you have to be 18 to sit? That was the case two years ago for me...??
One of the reasons i was even hired at all was because of my Intermediate EMT status. Being as young as i am (or so i was told) i showed a deeper understanding of my situation (meaning most companies simply dont hire under 21 these days with a majority preferring no one under 25) Had i gone ahead and taken Paramedic as opposed to that middle step, i probably wouldnt have been hired at all.
I too have run with a volley squad for a number of years, but being on your own in a rig with just you, your partner, and a patient is something all together and wholly different than third riding and taking BPs to help out the crew youre riding with. Frankly, someone willing to practice as a medic without any on the job experience as at least a Basic scares me. Book knowledge is very important please dont mistake me, but experience is something all the texts in the world cannot make up for, particularly in emergency medicine where rarely is one run the same as the last.
Lastly, im begging, wait until you graduate high school to actively seek employment in EMS. I understand the desire to practice while stuck in class, i was there once too, but frankly I wouldnt want a partner whose more concerned with their geometry exam on monday than the patient