Loss of bone density and muscle mass (muscle atrophy due to lack of use) are the primary causes for the elderly's diminished/shrinking frame. Fractures also can cause stooping and other posture problems that diminish the bodyframe in terms of height. People typically lose about half an inch each decade--starting at around age 40 (!!), with a faster rate of shrinkage after age 70. Senior citizens may shrink as much as three inches! Yikes. So enjoy it while you can; keep your bones and muscles strong through vitamin D, calcium, a balanced diet, and especially regular exercise.
Two types of exercises are important for building and maintaining bone mass and density: Weight-bearing and resistance exercise like jogging, walking, water-aerobics, stair climbing, and dancing. The other type of exercises are activities that use muscular strength to improve muscle mass and strengthen bones. One has to be careful as certain movements like twisting of the spine, high impact aerobics or bending from the waist can be harmful possibly risking a fracture.