Cells replicate a specific number of times and then die. Happens again, and again in lab experiments.
Structure of DNA is altered as people age. Due to alterations, DNA is not read correctly and results in transcription and translation malfunctions. Results in aging/illness/cancer directly, or indirectly.
normal wear and tear causes cells to function improperly
Free Radical Theory
Lipids in cell membranes are exposed to radiation or "free radicals"; cell membrane ruptures and cell dies.
Nutritional Model Theory
Lean mass, as opposed to adipose tissue results in greater health
Collagen Theory of Aging
As we age, collage ages too. Causes hypertension and other organ malfunctions