Here are some commonly asked questions, and their answers. It is at least four years away. If you really want to start earlier, ie in high school, do something interesting other than science. It doesn't really matter what it is, just do something you like. You'll get plenty of science in college.
Science is important.
Understanding basic scientific principles is vital to the practice of medicine. Knowledge of physics and chemistry will get you a long way in life, not just in medical field, but in nearly all of life's endevours. I am not saying that you shouldn't study science, but you should be getting that as integral part of your high school education. If you are looking for additional subjects to study, the humanties should be foremost in your mind. I am X years old.