Hi Dave, Im Brian. I am also 17 years old and I am currently going through the same about where to start off. I live in NY, many different regions have different protocols. You may start your EMT-B classes at 17 years of age, but you cannot take the written test until you are 18. In my area, the different levels of training are as follows:
CFR-Certified First Responder-- One step below an EMT-B and you are eligible to take this class at your age.
EMT-B-
EMT-CC
EMT-P
My area does not do EMT-Intermediates, but your region might.
I am currently an observer at my local Ambulance service to try and gain experience before I start my classes. You should check into that in your area. Most agencies do accept applications for observer only at 17 years old and the time you spend really pays off.
Good Luck!