Is 19 years old late to start MMA?
Not at all especially if you are not necessarily interested in becoming a fighter. MMA and other fighting arts are a great way to stay in good physical shape along with giving you some skills to help protect yourself better. Resuming martial arts at 19 till I was in my 50s while in the military along with doing some fighting arts in between paid off for me health wise. My weight was never a problem then, I could easily pass all my fit testing requirements in the military, and later after retiring I look 15-20 years younger than I am and am not on umteen medications like many of my friends are now and don't have near the health issues.
Since you don't say what your martial arts background is, I'll assume you don't have any. In this case, your best bet is to find a good MMA gym and spend as much time there as possible. If that's not an option, cross-train in BJJ and either Kickboxing or (western) boxing. That will give you a solid base to build on later. Keep in mind that like with other pro sports, the prime competitor age is trending in the 20s. You should expect to spend a couple years training before you're good enough to compete, if that's what you're aiming for. (If you just want to _learn_ MMA, 19 is plenty young.) If you want to make it in something like the UFC, then expect to train several days a week from now on, ideally at a gym known for sending folks to MMA events.
Not too late
I am 26 and I want to start taekwondo, so my answer is no, you're not too old. Don't limit yourself, you're never too old to l Learn anything.