Nope. Stupid idea. First, make it through the pre-reqs. Pre-meds drop like flies when they realize that the treatment of the sciences they got in HS pale in comparison to the college-level weed-outs. Even APs don't go into the detail of many college courses.
Second, you haven't a clue what you will want to do in your 20's. Human beings are plastic creatures, and the entire point of college is to explore other areas and fields, hopefully finding something about which you are passionate. As a HS student, you aren't there yet.
Third, cracking USMLE books now will be a waste of your time, as you probably won't understand 90+% of what is covered (A&P, Biochem, Neuro, Pharma, etc., etc.), since you haven't had the requisites yet.
Fourth, the sciences you are studying now aren't necessarily static - for instance, most of the college level kids I've talked with still think acid-base is regulated by the Henderson-Hasselbach approach. If you ask them about the physical-chemical approach (Stewart model), you get deer-in-headlights silence from them, despite it being more accurate and intuitive (although more math-heavy).
The bottom line is: enjoy HS, enjoy your summer, and don't try to grow up into a doctor quite yet. Enjoy being a kid while you can.
