IMO it's better to get experience in a particular area of mma instead of just jumping right into it. You probably will not learn as much valuable technique if you begin right away training at an mma gym. Either jiu jitsu or muay thai would be great starting points. Once you have gained some experience in one or both of these areas you can look into learning different techniques that will help you in mma. It is a longer process, but you will learn much more and you will definitely be better off in the long run. Good luck.