Three score and ten.
Excluding infant and child mortality, the average "natural" life span seems to be about 70 years. It has remained so for several thousand years. It shows little sign of change. Hard work and stress appear to increase rather than decrease longevity.
D000328:Adult; D000368:Aged; D001315:Australia; D005197:Famous Persons; D005260:Female; D049668:History, 15th Century; D049669:History, 16th Century; D049670:History, 17th Century; D049672:History, 19th Century; D049690:History, Ancient; D049691:History, Medieval; D006801:Humans; D007226:Infant Mortality / Q000266:history; D008017:Life Expectancy / Q000266:history; D008136:Longevity; D008297:Male; D008875:Middle Aged; D012737:Sex Factors