What does Genesis 5:28 mean?

Lamech is the ninth generation from Adam, despite being born many hundreds and hundreds of years after Adam. Using the ages given in this chapter, Adam was still alive when Lamech was nearly sixty years old! That's an important part of the context of this passage. The next chapter will describe mankind as deeply depraved, causing God to send the flood (Genesis 6:5). Clearly, humanity could not blame their sins on forgetfulness, or having lost their heritage. At the time of the flood, there would have been men and women alive who personally knew Adam, or his sons and daughters. The evil of mankind was not because we had forgotten about God, but because we had chosen to reject Him.

This verse also breaks the normal pattern of the chapter, adding Lamech's prophetic comments about his son, Noah, in the next verse.

Lamech is the first of the patriarchs to actually "die" before his father. While his grandfather, Enoch, was only on earth for 365 years, he was taken by God prior to death. Lamech will die at the age of 777, five years before his father, Methuselah.