A 100-year-old person can have a perfectly sharp mind while their biological clock says they are running out of time.

Centenarians who remain mentally sharp until their final days still possess a separate biological clock that tracks the decay of their organs. The mind and body are often expected to age at the same rate, but this research shows they can operate on completely different timelines. A specific DNA marker called GrimAge measures the biological age of blood and tissue regardless of how healthy the brain remains. This peripheral aging score accurately predicts mortality even when neurological tests show no signs of dementia or cognitive decline. Life expectancy at extreme old age depends on this internal countdown rather than how well the brain is functioning. Medical professionals may eventually need to treat the body and the brain as two separate patients with their own unique expiration dates.