Life expectancy is calculated by computing average age of death, so given that about half of children died before their teenage years the averages are skewered downward and don't tell us much at all about how long people lived at all.

Post-childhood human life expectancy is was stable at around 70, before climbing upwards during the industrial revolution. Consequentially, people who were having mid-life crises were having them more or less the same time. Plus, in a hypothetical society where people face the horrible prospect of dropping dead at thirty, do you really think they would be asking existential questions about what they were doing with their life at any point?