I didn't say fur was a negative thing. It depends what niche the animal is filling. Lack of fur makes it easier to cool down which means you can run for longer periods of time without collapsing. The average human can keep walking/running a lot further than the average gorilla.
Combine the ability to run for long distances with the ability to remain cool while doing so and you end up with a very deadly predator.
Also, to my best recollection, "prehistoric" fossils are few and far between. It cannot be stated on such a small sample size how old they were typically when they died.
Even if we did not have lots of fossils from pre-historic times, we have plenty of skeletons of people who have died in historic times. Up until very recently, life expectancies for a human anywhere in the world were quite short. It's only since the rise of modern medicine that living past even the age of 40 can be taken for granted.