Wear and tear on a body throughout a lifetime affects the skeleton. Arthritis of the spine and joints can reflect increasing age. Scientists also recognize many other clues to aging, such as the appearance of the rib ends and the cartilage that joins them to the sternum. In a young adult, the rib end walls are thick and smooth, with a scalloped or rounded edge. In an older adult, the walls are thin, with sharp edges, and the rim often has bony, irregular projections.