Man get into MMA as soon as you can. It's a great way to get fit. Two things though. First of all i would be finding a gym with some heavy guys to train with. I'm a heavyweight myself and finding sparring partners can be a real pain in the arse. Secondly before you jump head first into mma training it would be a good idea to have some bjj training and possibly some muay thai lessons or other striking. Not to a great degree but enough to maybe have a grade or two so you can hang with the more experienced guys for a bit. Take it slow, sounds like you got plenty of time.