Why do people gain weight when they geet older?

Less muscle/exercise: As we get older, our muscle mass decreases and thus burns off less energy/food. If we burn less and yet eating/consuming the same amount of food, we gain wt. Also, because physically we are able to do less, we use less energy from foods. So stay physically active as much as you can, eat less junk food, see doc regularly, sleep well, and live well. We all subject to progression of time..Good luck.