We evaluated the process of senescence in long- vs. short-lived individual, based on a “prognosis” score that aggregates multiple measures of aging physiology. First, based on our physiological measurements, long- and short-lived individuals are indistinguishable at the beginning of adulthood. Second, soon after the onset of reproductive maturity, short- and long-lived individuals diverge rapidly. Overall, short-lived individuals experience faster physiological aging than long-lived individuals. In addition, short-lived individuals often die “prematurely”, while still healthy-appearing. Third, we discovered that long-lived individuals spend a disproportionate fraction of their lives in highly senescent, ill-appearing states. This extended “twilight period” of low physiological function has the paradoxical effect of reducing the overall average physiological health of long-lived individuals to below that of short-lived individuals.