It's obvious nowadays in the era of a sofa and Netflix, not 4000 years ago where 9 out of 10 new born kids die and those who survived generally didn't make it until 25 years old, and where the primary issue of people was what to eat the following day and in case no tribe attacks them in the middle of the night if they would survive to the bite of that scorpion.
Almost half of all births ended in death before the age of 5, greatly lowering the average.
When infant mortality is removed, evidence seem to show averages of life expectancy for 3000 years ago to be around 52, give or take 15 years.
When you're cities of 20-40k people 4000 years ago, there's quite a bit of admin work that has to be done - it's not all small farmer villages or hunter-gatherers. Ancient Sumeria was quite advanced.
That's a lot of assumptions about life 4000 years ago when the article provides evidence of someone doing admin work instead of worrying about food, "tribe" attacks and scorpion bites.
