I am trying to lose weight, about 40 pounds. There may be some temporary drooping of your skin when you lose the weight, depending upon how fast it's lost. Only time will help. Of course, adding insult to injury, we naturally sag and wrinkle with age as the connective tissue that keeps our skin taut deteriorates. Here is the reason exercise won't tighten your skin.
Muscle fibers are the main tissues in our bodies that respond to exercise.
That's the bad news. Here is the good news. Exercise can tighten the muscles under your skin and help flatten your abdomen. The sagging skin you do experience will, for the most part, disappear in time since at your age you still have plenty of skin tightening connective tissue. And the health and other cosmetic benefits associated with maintaining a desirable weight will be far more significant and noticeable than a bit of a belly sag.