Why 120 can look like a limit
The human body does not have a single timer that switches it off at a certain birthday. Instead, aging gradually weakens several systems at once: cells accumulate damage, tissues repair themselves less effectively, and organs have less reserve to recover from illness or injury. These changes raise the chance of death, but they do not create a precise age at which survival becomes impossible.
The figure of about 120 is best understood as an estimate of how far the observed human lifespan might extend under extraordinarily favorable circumstances—not a biological deadline. Estimates of an upper limit draw on patterns in lifespan records and on how rare it becomes to survive to extreme ages. With very few people reaching those ages, the evidence cannot establish a hard ceiling.
Why the last years are especially difficult to reach
Surviving into extreme old age requires more than avoiding one fatal disease. A person must weather many years of increasing vulnerability, when an infection, fall, or other setback can be harder to recover from. The body’s systems are interconnected, so a problem in one area can strain others that have already lost some of their capacity.
That makes exceptional longevity a matter of unusually favorable circumstances across a long stretch of life. But it does not tell us whether a person could live beyond the ages seen so far. A limit inferred from rare observations is not the same as a limit built into the body. Until evidence shows otherwise, 120 is a useful point of reference, not a confirmed stopping point.
