calling people or belief systems names doesn't prove anything. Why should I believe what some guy from the mid-1800s said about how the world came into being, over people that may actually have been around?
And the stuff in the Bible is repeated across several different cultures, indicating it's not just from the Bible. For example, the idea of someone doing something to plunge existence into an imperfect world is reflected in Greek mythology, as is the global Flood, which is actually reiterated in many ancient religions. Actually, the Bible isn't even the only religion that suggests that people lived longer before the Flood. In the epic of Gilgamesh, a king is said to have lived for 43,200 years.
This would make sense if everyone descended from someone who remembered the Flood. It does not make sense at all if the Bible was made up, because unlike now, people could not communicate cross country easily.