You often hear that someone died “of old age.” That is not exactly true. People die because some vital body part fails to function properly. This may be the brain, the heart, etc. Sometimes the body part is “defective.” Sometimes damage to the body part occurs because of a bad injury. There are some body parts that, when damaged, can harm other body parts, until the body cannot stay alive any longer. When someone dies “of old age,” there are often several worn-out body parts, and one of them just gives out.
Answer provided by Dr. Universe