What does Genesis 5:17 mean?

The ages at death of the patriarchs listed in this book of Adam thus far are as follows: Adam-930, Seth-912, Enosh-905, Kenan-910, and now Mahalalel-895. The presence of physical death is, so far, the most obvious consequence of the fall. Regardless of how long these early patriarchs lived, they all died. The only exception seems to be Enoch, who found himself gone from this life and face-to-face with God all the same (Genesis 5:24). The repetitive comment, "and he died" is no accident.

When one lines up the birth and death dates of these patriarchs, it becomes clear that there is a significant overlap. In fact, other than Enoch, the only men in this line who are not still alive when Noah is born are Adam and his son, Seth! And, as we will see later on, Noah's father, Lamech, was born more than 50 years before Adam's death. This is crucial for understanding how deep the effects of sin were in the pre-flood world. Despite having eyewitnesses to God's creation, or their direct descendants, mankind will spiral out of control until God removes nearly everyone (Genesis 6:5–8).