I went into college with 46 hours of AP credit, compulsively squeezing in every class I could my first year. I got good grades, etc, but I would not advise it under any circumstances for several reasons.
1) You need to have fun. If you don't want to have "fun" per se, at least have a balanced life. Don't go killing yourself over academics (ie, get good grades, but don't try to get them in graduate level courses).
2) You don't want to frontload your schedule with the most relevant courses. Think of it this way, OChem, Physics, GenChem, Genetics, etc will all matter for a) your AMCAS transcript and b) your MCAT. You want to spread them out sufficiently prevent overloading. It's also VERY handy to be taking one or two of these courses going into the MCAT your third year. For example, I had Biochem and Physics my third year, so I didn't have to do much extra preparation for those portions of the MCAT.
3) You're a freshman. Odds are, you're still not 100% sure this is your path. You may be 99% sure now and fall in love with another area later. I'd emphasize things like doctor shadowing, ER volunteering, etc first. That way, you'll know you love it and be more motivated academically or know it's not for you and spare yourself the agony of premed courses.