hey littleone,

Im also 17, about 4'11 and coming in about 90 right now I have to agree with ninja-raiden in that grappling arts arent the best choice.

Does it have to be a martial art? Ask yourself what you want. If fitness and defence skills are what you are looking for, take self defence classes and aerobic classes. If you want an education and a more technical base, then a martial art
(preferably striking).

As for gaining weight, do you eat healthy i the right amounts? If so, dont worry about gaining weight. You are the weight intended for your frame. If you are an irregular eater who isnt eating the best and losing some pounds, stop it immediatly and eat healthy.

NEVER think that your size can stop you from doing a martial art.