During these periods, an excessive amount of weight gain causes an increased number of fat cells. Once a fat cell is formed, you generally cannot get rid of it. As a general rule, as you grow older, your metabolic rate slows down and you do not require as many calories to maintain your weight. People frequently state that they eat the same and do the same activities as they did when they were 20 years old, but at 40, are gaining weight. This will happen.
Metabolism does slow down with advancing age.
Gender Gender is also an important factor. Males have a higher resting metabolic rate than females, so males require more calories to maintain their body weight. Additionally, when women become post-menopausal, their metabolic rate decreases significantly. That is part of the reason why many women start gaining weight after menopause. Activity level Active individuals require more calories than less active ones.