This will be a fun essay. Very short, too.
We read in Genesis about the ancient Patriarchs: the paternal lineage from Adam to Noah to Abraham. Genesis lists them, without offering much detail about these people. Read chapter 5 now. Then refer to this diagram (courtesy of www.conformingtojesus.com) which shows when each of these patriarchs lived.
Noah was the 10th generation from Adam; counting years as specified in Gn 5, Noah was born in the year 1056 (from the creation of Adam). We note that all of Noah's ancestors died prior to the flood. The famous Methuselah died the same year as the flood - did he perish in the flood or did he die just before it began? We don't know.
Methuselah is famous as the oldest man who ever lived. An old-time saying is, "As old as Methuselah," referring to something or someone very old. At 969 years old when he died, he was a mere 7 years older than his grandfather Jared, and a mere 19 years older than his grandson, Noah.
The lifespans of these patriarchs were extraordinary. Then God saw the evil of humankind and He decided to shorten our lifespans:
3 Then the LORD said, "My spirit shall not abide in man for ever, for he is flesh, but his days shall be a hundred and twenty years." (Gn 6:3)
Did the patriarchs really live to be 900+ years old? You can decide.
We note one of the Patriarchs, Enoch, had something interesting happen to him:
22 Enoch walked with God after the birth of Methuselah three hundred years, and had other sons and daughters. 23 Thus all the days of Enoch were three hundred and sixty-five years. 24 Enoch walked with God; and he was not, for God took him. (Gn 5:22-24)
Enoch walking with God is understood to mean that Enoch was a very holy man, with a very close relationship with God. It is also believed that he did not die, but was taken to heaven by God as a reward for his holiness:
5 By faith Enoch was taken up so that he should not see death; and he was not found, because God had taken him. Now before he was taken he was attested as having pleased God. 6 And without faith it is impossible to please him. For whoever would draw near to God must believe that he exists and that he rewards those who seek him. (Heb 11:5-6)
After Noah, human lifespans slowly reduce in length. Abraham lived a "mere" 175 years. As a last point of interest, we note that there were two Enochs and two Lamechs mentioned in these early genealogies. Our list of the Patriarchs is the lineage of Adam through his son Seth, generally understood as being a lineage of those who worship the true God. In contrast, Gn 4 tells us about a different lineage through Cain, generally understood to be a lineage of those who do not worship the true God and who do evil. Gn 4:17 says that Cain's son was also named Enoch; then Cain built a city, the first city, and he called the name of the city Enoch, after his son. This in contrast to Seth and his son, Enosh, who "called upon the name of the Lord" (Gn 4:26). Both use a name, but for Seth/Enosh, it is the Lord's name in worship, while for Cain/Enoch it is the name of a self-styled city. Again, in Gn 4:19-24 we read about Cain's descendant Lamech: he was the first polygamist and a murderer like his ancestor Cain. The lineage of Cain was cities, metalwork, amusements, polygamy, murder. Meanwhile the lineage of Seth includes Enoch, who walked with God, Noah, who found favor with God (Gn 6:8), and Abraham, the Patriarch of God's Chosen Ones.