Gurven, Michael & Hillard Kaplan (2007). “Longevity Among Hunter-Gatherers: A Cross-Cultural Examination.” Population and Development Review, 33(2), 321–365
If you made it past age 5 as a hunter-gatherer you’d likely live to 50-60 years of age.
It’s also worth noting that, while this is (I think) likely the most cited paper on the topic, all the observed societies are from the 20th century. So we can’t necessarily extrapolate from that that hunter-gatherers 300,000 years ago fared the same.