Why do 72 year olds shrink?

Answer 1

The most common reason why people shrink as they get older is osteoporosis - loss of density from bones (especially in the spine) means that they can fracture or crumble, which is painful and results in loss of height. This is also the reason why some senior citizens develop what is sometimes called a "Dowager's Hump" - a stoop, so that it appears as though they're always looking at the ground.