Firstly, well done for showing such enthusiasm.
The thing to do is to go to uni and major in maths - you'll then see how different university maths is from high school maths - this may change your mind or, maybe, not...
You can always become a maths teacher staright out of uni - perhaps in the states you can even do a degree in it (???) - though the maths degree seems the best choice for you.
If you want to lecture, you have to do that PhD. You then have options, either stay on as a postdoc - doing research for as long as possible; become a postdoc with some teaching; get a tenure track position which will involve a lot of teaching (and possibly a job after the tenure); or look straight for a lecturing job.
Best not to plan these things too far in advance - just keep up with the maths and you'll be fine