You can get stronger without adding lots of muscle mass... think of a gymnast instead of a body builder or strongman. There really isn't anything wrong with getting stronger and I would encourage it at any age, it's good for the bones too. I would track calories with myfitnesspal.com and set it to lose a 1lb a week, avoid starvation diets and silly things like that. No amount of situps will burn away the belly. If you slowly chip away at your bodyfat percentage while eating healthy amounts of protein/carbs/fat (think "clean eating") I bet you can get shrink the little bitty belly ya got. I've lost ~85lbs and I have a saggy pouch that is starting to tighten up finally and I hope to get rid of it completely when I get down to 180 or less... currently 5'11 and 200lbs.