I think as a young man your aspirations are exemplary. I would get involved in whatever NRA activities are available in your area. You are in that transitional period between 17 and 21 - use this period to learn and improve. If there are community college courses on law or POST training attend them.
As you can afford it take classes from any of the quality schools of instructors. Work up to perhaps assisting instructors as you gain experience.
Take a college class in teaching. Teaching is a study of itself, it's not just showing someone how to do something, it is how you go about letting them learn. I'm sure after 12 years of school so far you probably understand that.
Once you are 18 you might take a security guard course. Whether you work in the field or not you will usually learn stuff.
There is also always the Army. Though my advice on that is go ROTC and be an officer.
Good luck in your endevours!