Right - if you look at a lot of the locations they're on relatively high ground and in hill country so the rising and setting of the sun relative to hills or other landscape elements was what they did, and they marked off quite sophisticated cycles. Given that a 22 year cycle needs multiple observations to track, and given that the life expectancy was probably somewhere in the 40s the achievements are pretty amazing.
Life expectancy is commonly misunderstood. First, the full term is actually "average life expectancy". It was low because the huge number of child deaths simply drove down the average of the whole population. People frequently lived way into their 70s or 80s or 90s, as they do now.
Secondly, it's the average expectancy, not lifespan. The expectancy is a statistical measurement of how long one is likely to live from the time of one's birth (or from a given age). At birth, the life expectancy would low. But if you reached maturity, the life expectancy would be quite high.
In other words: The average life expectancy before the 20th century was very low. The average lifespan of mature adults was not a lot lower than today.
If life expectancy was in the 40s, survivors of childhood could probably expect to live significantly longer than that. Child mortality skews life expectancy downwards.
Plenty of people reached 60+ and some reached 90+ back then. Don't forget identical biology bad healthcare so lots of people died young and or in childbirth.
