We can see in the bible that a lot of generations from Adam live around 500 - 1000 years. Right now, with an average life expectancy of 70, we consider 50-60 years as old age.
In Genesis 17:17, Abraham was thinking that how could his wife be pregnant at the age of 90 (Abraham was 99 at that time). From that sentence, I understood that Sarah was old enough to not bear a child.
I was thinking about what was the period of childhood, youth, adult, and old age during the time of Abraham. And also at the time of Adam.
Any thoughts? And how that shift in age group would have happened from Adam to Abraham?