Middle age spread

This graph shows the general rule for both sexes that you get heavier as you get older. Slower metabolisms and increasingly sedentary lifestyles as you age inevitably take their toll. Most people don't have the genes or the discipline to defeat this unfortunate accumulation of excess padding. This phenomenon is reflected in the joke:

Q. How do you turn a fox into an elephant?
A. Marry her!

To be fair, most men develop a paunch as they get older and they don't have the excuse of carrying a child! This is known medically as an intestinus guinness, or in common parlance, a beer gut!