physical therapist...?

Absolutely without a doubt. Studying anatomy before college will be invaluable for you. Physical therapists have to memorize almost every muscle, joint and bone and their functions range of motion, etc. To have a jump start learning the names and basic movements and functions would be a great help to you in college. As for other subjects, any subject dealing with speech or communication would be a great help, maybe even learn a new language being bilingual makes you much more desirable once you begin looking for a job.

The only other thing I can think of to recommend right now is volunteering at a hospital or home health care center in your area. Volunteering teaches you first hand what being a physical therapist really is like, and you can get a more personalized view of what areas you would like to study. Hope this helps!

P.S. If your high school does not have classes that are going to prepare you for college, you could try dual-credit classes at a local community college. Dual-credit classes are really nice because you get high school and college credit at the same time. That makes college a whole lot easier, because you've already gotten some courses out of the way.

Anatomy and Physiology are great courses to take if interested in the field of Physical Therapy. Also, you will need to learn the Actions, Origins, Insertions, and Nerves of all the muscles so if you can study that, it would be beneficial. Also, physics is used quite a bit in the field or well. You will have a better understanding of certain concepts.

See what the college you are going to for PT/PTA have as the required general ed courses. That should give you an idea of what to select for you senior year of high school.

Next, although someone else (who said they were a PT) stated that you don't need college to be a PTA, the national professional organization for PT/PTA seems to think otherwise: http://www.apta.org/AboutPTAs/