The answer I believe in part lies in the state of the earth when God first Created it, compared to the sin wrecked world we live in today.
When you look at the age of the Patriarchs (Adam's descendants) in Genesis you will see two things. One, is that from Adam to Noah the average life span was somewhere in the neighborhood of 900 years. These people lived in a very different world than we do today (this was at a time before the flood described in Genesis). God Created the earth perfect. But when Adam sinned this world began to decay.
Then when the flood came, things really got wrecked. Some Creationists believe that the pre-flood vapor canopy (the firmament in GEN 1:6 ) would filter out radiation, and hold in incoming solar heat making the earth a warmer place to live. This "expanse" separated the "waters above" from the "waters below" in the Creation week. I believe that the firmament may have collapsed at the time of the flood.
As a result harmful radiation can enter the earth more easily than before, bringing with it all kinds of damaging effects.
The life span of man has been declining since the flood. The average age of man quickly dropped to less than 100 in the 200 years after the flood.
Some critics claim that the 900 years of life mentioned in the Bible were not literal years. They claim that back then people counted each month as a year. They claim that you have to take the age given in the Bible and divide by 12 months.
This is wrong for many reasons. The Bible tells us how old the patriarchs were when their children were born. Cainan was 70 when his son was born. If you divided the age by 12, then that means he would have had a child at 5 years old. - This is impossible.
Also Moses compiled Genesis. He could clearly differentiate between a month and a year. He did so many times in his writing.
Also, when Jesus came to earth he taught us many things. If the Patriarchs did not live as long as the Bible claims then Jesus would have told us.
The ages given in Genesis are literal years.
Rather than evolving, we are degenerating. And will continue to do so until Christ returns.
Leibling.
