The old MCAT has retired, but the scores are valid for 3 years as usual. However, some medical schools have already stated their preference for new MCAT scores over the old ones. So, you should make sure with the medical schools you're applying to if your old MCAT score is valid for that entering class or you would need to write the new MCAT and submit that score. But as of now, most Medical schools will continue accepting the old MCAT score. Acceptance of new MCAT score mandatorily will likely be seen taking effect for the 2017 entering class. AAMC will have history of all the MCAT you've taken so far. They have mentioned that it is not possible to compare scores between old and new MCAT. So, don't worry about old MCAT score pulling you down in face of better performance in the new MCAT.