The period of Arabian history leading up to the Arab conquests has become a fascination of mine. One odd thing I've noticed, is that many of the figures attested from this period seem to live rather long life spans relative to what I've always understood as being the average lifespan of a person in this time period. For instance, Omar ibn al-Khattab is attested to have been born around 583 CE and died 644, making him around 61 years of age at the time of his death. This also seems to be true of Muhammad, Abu Bakr and a few other figures in this time period as well.
So, what I'm wondering is this: is this an accurate lifespan for someone in this part of the world around this time? Or is it the result of poor documentation/exaggeration? Would this have been an extrordinary circumstance? Furthermore, how accurate is the classical historical image of men being considered old for their time simply for living into their forties?
That's not how average lifespan/life expectancy work. For example an average life expectancy of 47 doesn't mean everyone dropping dead after age 47, it means many infants and children die due to diseases (which they are far more vulnerable because of immature immune system) and lack of healthcare and they are bringing down the average significantly. Once someone gets past childhood then it would not be unusual for them to live to old age.
See this answer from /u/Roxinos for more in-depth explanation.