Old people can hear low tones fairly well, but their ability to hear high tones decreases. The capacity of tissue and bone to repair itself is slowed, as is cellular growth and division. Bones become brittle and skin loses its thickness and elasticity, causing wrinkles. As brain cells die some capacity for memorization and learning is lost. Breathing becomes difficult, and hardening arteries circulation to worsen and blood pressure to rise.
Joints lose their mobility and deteriorate from constant wear and pressure.
These are not all of the changed to the body that are brought about by aging, but these are the major ones. There is hope in modern medicine, though. Through the use of new technologies and drugs some of these changes can be slowed or prevented. Process accelerated by overuse of alcohol and other drugs, repeated blows to the head. Process accelerated by injury, obesity.