What does Genesis 5:14 mean?

Kenan, the fourth generation from Adam, dies at the age of 910 years old. The final ages of those listed thus far are as follows: Adam-930, Seth-912, Enosh-905, and Kenan-910. Based on the ages given in this passage, Kenan lived several hundred years in common with Adam, and quite a few years in common with Noah. This, again, supports the idea that mankind had a clear and unbroken understanding of their own history in the years leading up to the flood.

This makes the sin and evil prevalent in the days of Noah all the more despicable. When the flood came, there were men and women alive who had spoken with Adam and his immediate children. The real history of man had not been lost, and there were still those alive who knew what the world was like when it was very young. But, as the next two chapters will explain, only Noah and his family were going to be spared from judgment.