These verses describe the next five generations. We should note that these people had many more children than those mentioned here. We read of each one mentioned here, “And he fathered sons and daughters.” They all grew old and therefore they also had a long period of being able to have children. It is notable here that Mahalalel was 65 when he fathered his first son while Noah was already 500 when he fathered his first child. So the fertile period in humans was very long at that time. We see here that mankind expanded quickly, and how therefore different generations and families were quickly formed.
6 When Seth had lived 105 years, he fathered Enosh.