Damn nature, you scary!

A lot of the time averages are skewed by the amount of child deaths. That may not be so. It really depends on the conditions.

The average lifespan of a wild chimpanzee is actually very similar to the average lifespan of a wild human, seeing as how we're so closely related. And the average lifespan of a chimp is about 33 years.

Again alot of that is dependent on conditions such as type of foods readily available, climate, other wildlife. It really is not uncommon for adults to live up till their 70s in primitive cultures. Granted not everyone will and infant deaths have a higher rate but it's not uncommon. However it is uncommon in societies with enforced ignorance and social classes where the betterment of a few is placed in vast priority over the rest.