Man’s Lifespan

Parts of the Bible refer to people who lived for hundreds of years. There are two theories. One says human beings cannot live for hundreds of years and that ages given in The Book of Genesis are based on a confusion between lunar and solar time, turning months into years.
So when the Bible says that Methuselah lived to the age of 969, it really meant about 80, which seems to make more sense. On the other hand, various men in Genesis became fathers in their sixties, which would make them five years old.
The other theory is that man’s lifespan was altered by God after the flood. In chapter 6 of Genesis, we are told that our days will number 120 years, but that was after the flood and all the really old men lived before it.