There is no reason to believe that the ages of the patriarchs were not meant to be taken literally. Those who study aging believe that there really is no reason why we are limited to living no longer than 120 years, other than the fact that we are.
Genesis 6:321st Century King James Version (KJ21)
3 And the Lord said, “My Spirit shall not always strive with man, for he also is flesh; yet his days shall be a hundred and twenty years.”