What does Genesis 5:7 mean?

Population growth is considered "neutral" in areas with low life expectancy when the average woman has three or four children in her lifetime. Imagine a world with much lower rates of disease or war, cleaner food, water, and air, and a dramatically longer natural lifespan. It's not unreasonable to calculate the population of earth exploding at an explosive rate during the generations described in this chapter.

In this verse, it's stated that Seth lived for "807 years and had other sons and daughters." More than likely, Seth had an enormous number of sons and daughters. Due to the long lifespans of these first generations of humans after the garden, the population of the world was likely increasing dramatically. Each couple could likely bear many children over the span of hundreds of years, seeing those children marry and have children and grandchildren and great grandchildren while they continued to have new children of their own.