When interpreting scripture it is important to consider it’s communicative intent. In other words, what were the authors trying to communicate their contemporary hearers (not us). Many of us make the mistake when reading scripture of thinking that the words were written to us. The words of scripture are definitely for us, and all people, but they were not written to us (see the About the Bible page). Many people may come to the texts of the bible looking for facts, evidence, etc. but in doing so we miss what the scripture was actually trying to communicate. We must also remember that we are dealing with ancient texts written in a time when ideas about things like dates were completely different from today, and numerical systems, and even written languages, were still in their infancy.
That said, let’s consider something like the problem of life span in Genesis 5. How could people have lived hundreds of years, and how could those men have fathered children at such ridiculously old ages? When considering the births of the children, I think it is important that we understand that the term beget, or the idea of becoming the father of, does not necessarily mean that that person is the father of the child that was born. In fact it is more likely that he is the grandfather, great grandfather, or great great grandfather. Those who recorded these genealogies likely only included the ancestors who lived lives of some type of significance, thus eliminating those who were less significant. So when it says that at age 187 Methuselah became the father of Lamech it doesn’t necessarily mean that Methuselah was Lamech’s father, he may have been his great great grandfather.
Of course this still leaves us with the more difficult issue of the very old ages. Hard to believe, right? At this point I think it is important to do some interpretive work, i.e. what is the author trying to say to the people. Specifically, what is he saying about God and people. If you look closely at the entire chapter of Genesis 5 we shouldn’t be distracted by the great ages of these men, rather we should be struck by one recurring phrase… “and then he died.” The significance of the Genesis genealogy is not how long these men lived, it is the fact that they died. The idea being communicated here is that the consequences of Adam and Eve’s sin is real. God wasn’t kidding around when he said “if you eat the fruit of the tree you will surely die.” And furthermore, it shows the serpent to be a liar, because he said to Eve “you will not surely die”, yet clearly people are dying. The phrase “and then he died” is repeated 8 times in Genesis 5. Only Enoch in verse 21 does not die, and the significant difference between Enoch and the rest of Adams line was that “he walked with God” (but that’s a discussion for another post). In Genesis 6 God makes it clear that most humans are not walking with him. Thus he limits the life of humans, because he does not want to “contend with them forever”.
I believe that Adam and his ancestors did live those long lives, but whether or not they did or did not is not the key issue, the significant issue is that they died. And that is what the author of Genesis was trying to communicate.