Biblical historians: why are the lifespans of people mentioned in the genesis accounts recorded as lasting so long?

Biblical historians: why are the lifespans of people mentioned in the genesis accounts recorded as lasting so long? * /r/AskHistorians

reddit.com

The question is quoted below. Click on the link to see the answer given by the historian.

Are there any theories as to reason for the records of extremely long lifespans (300-900+ years) of the people written about in Genesis?

  • Was it a cultural thing, to exaggerate things like that to make your bloodline seem more impressive (i.e. an indication of your family being more favored by God)?
  • Translation errors?
  • Did the author actually believe that their ancestors lived that long?

I know it's tough to speculate on the exact motives of authors writing thousands of years ago, but I'm fairly ignorant in this department. Are there any known explanations for why they wrote like this?