According to the ancient Sumerian tablets the kings "reigned for long periods of time before the flood, ranging from 18,600 to 43,200 years" from https://www.ancient-origins.net/myths-legends-asia/sumerian-king-list-still-puzzles-historians-after-more-century-research-001287
If that was true, then either certain groups of humans were able to live very long time, or they were aliens, or alien hybrids. Not all early humans were able to live such long lifespans. According to anthropologists the regular grunts died very young. It looks like only the kings in Sumeria as well as the important families in the Bible were so talented. It's interesting that there is quite a discrepancy between the Sumerian kings' lifespans and that of descendants of Adam and Eve. Makes me wonder, what if Sumerian kings were the aliens. I suspect, they got into their UFOs and left when the flood started, but the unfortunate humans or human-alien hybrids were stuck. Perhaps the gods indeed caused the flood in order to genetically modify the programming of human lifespan reducing it to 120 years because they feared the overpopulation of Earth would come much too soon. They had to drown the rest of the humans so that only the short-lived ones would procreate.