Actually it depends on how you exercise.
If you are doing lots of aerobic exercises regularly you will eventually start losing weight wherever you want it or not.
That's simply because with time your body, your lungs your heart, all your veins and capillaries will adapt to this regime and will be able to burn much more energy in a short period of time. Medically speaking your metabolism will become much faster.
And the opposite is also true - lack of exercise will eventually lead to obesity.
Thats because your body will adapt to the fact that you don't need to spend lots of energy and your lungs and heart will become less powerful.
So even slight overeating will lead to weight gain. That is happening to most people that become older and it's not because of age but because of changed lifestyle. I am not even talking about people that had never developed a fast metabolism during their childhood.
Gaining weight is a result of turning from a powerful car that can consume lots of fuel in a short period of time to an economy class car.