Paleolithic Lifespan

The lifespan of paleolithic man is a subject of considerable controversy on the internet and in pop-culture, largely politicized by dietary dogmas such as the paleolithic diet.

Physical evidence

Based on physical evidence of skeletal remains, the life-expectancy at birth of paleolithic man was roughly 20 years, only slightly higher than the typical life-expectancy of wild chimpanzees and probably lower than chimpanzees in more ideal wild environmental conditions[1], which is roughly the 33 years life expectancy at birth of modern hunter-gatherers.
Ultimately, environment, including regular food supply and low predation, is one of the leading factors in life expectancy:

"Our findings show how ecological factors, including variation in food supplies and predation levels, drive variation in life expectancy among wild chimpanzee populations [...] They also inform the study of the evolution of human life history, helping us to imagine the conditions that could have changed mortality rates among our early hominin populations." -Brian Wood, assistant professor of anthropology at Yale University[2]

This appears to be true of both chimpanzees and early humans, who were subject to strong environmental pressures (see #Predation).

Paleo-diet propaganda alleges that people misrepresent paelolithic lifespan by quoting averages including infant mortality (which was high by modern standards), but that adults routinely lived into very old age thanks to the miraculous grain-free diet, and that the advent of farming shortened average adult life expectancy due to dietary reasons. There is no evidence for these paleo-diet claims.
While inclusion of infant mortality lowers the total numbers (for example, life expectancy of 20 at birth doesn't mean that you won't live past 20, but that the average person won't), the life expectancy at 15 is only another 20 years at most, for a total under 35. This is based on both prehistorical skeletal evidence and projections from Neolithic data[3].

Higher numbers that are referenced among paleo-dieters and optimistic anthropologists (who prefer to romanticize ancient humans as they do with hunter-gatherers[4]) are based on extrapolations from methodologically problematic modern surveys and dramatically conflict with actual physical evidence.

It is usually reported that Paleolithic humans had life expectancies of

15–20 years and that this brief life span persisted over thousands of generations (Cutler 1975; Weiss 1981) until early agriculture less than 10,000 years ago caused appreciable increases to about 25 years. Several prehistoric life tables support this trend, such as those for the Libben site in Ohio (Lovejoy et al. 1977), Indian Knoll in Kentucky (Herrmann and Konigsberg 2002), and Carlston Annis in Kentucky (Mensforth 1990). Gage (1998) has compiled a set of reconstructed prehistoric life tables with similar life expectancies[...] Mortality rates in prehistoric populations are estimated to be lower than those for traditional foragers until about age 2 years. Estimated mortality rates then increase dramatically for prehistoric populations, so that by age 45 they are over seven times greater than those for traditional foragers, even worse than the ratio of captive chimpanzees

to foragers.[5]

There is extensive speculative criticism of the physical evidence, including hypotheses on potential biases in preservation and speculation on evolution of longevity, but nothing that provides actual evidence contradicting available physical evidence.

However, even based on the inappropriate hunter-gatherer comparison and optimistic averages of 33 years at birth, and accounting for infant and childhood mortality, life expectancy at 15 was still below 55 total, very low by modern standards (77-81 total).