You forget that life expectancy for native populations aren't due to them to not living long lives, but more due to the fact they have more deaths at childhood (due to stuff like bacteria infections and other diseases we now prevent). So you have a big chunk of population dying young. Also these cultures can be more violent and often have wars killing a big chunk. But past that bump it's not as short as the average (it's far larger). For example the Native Americans if one of them lived to 40, he could expect to live to round 70. https://www.reddit.com/r/AskHistorians/comments/12o4py/what_...

70 is easily a cancer age. Going by the current research at https://scienceblog.cancerresearchuk.org/2015/02/04/why-are-... one can expect 3/4 people over 60 to have cancer. And it's increasing.

So yeah the not living long enough doesn't really hold water. Also juvenile cancers weren't really a thing at all until the modern world (more likely bacterial infections until we discovered penicillin were more likely for juvenile deaths).

Cancer increases with age, but also with smoking, drinking, pollution, bad diet, obesity, lack of exercise, and exposure to viruses. I wouldn’t be surprised if people living in a tribal society had lower cancer rates even if you corrected for age. On the other hand, if they did get cancer, survival rates would be much lower.