What does Genesis 5:18 mean?

Jared fathers Enoch at the age of 162. Enoch becomes the seventh generation from Adam through the line of Seth. Jared and Enoch will be the last of the patriarchs to depart well in advance of the flood. The next two men in line, Methuselah and Lamech, will both pass shortly before—or, in the case of Methuselah, possibly when (Genesis 5:27)—God sends His epic judgment to earth.

Given the long lifespans of these patriarchs, most of the men listed died a (relatively) short time after their fathers. Jared and Enoch are the notable exception, in that Enoch will be "taken" by God in some way long before Jared's death (Genesis 5:24).

The next verses will repeat the common themes of this chapter. Jared will have more sons and daughters than just Enoch, meaning the population of earth must have grown extremely quickly. Also, Jared will die, like all men since the fall. The only patriarch not explicitly said to die will be Enoch, and even he will be "taken" by God. Regardless of long life, each person is destined to meet God someday.