The 6,000 year thing isn't Biblical, although it's assumed by churches that it it. 6,000 years is a number someone came up with in (I think) the 1,700s by counting all the "begats" and assigning a certain number of years per generation. Nothing in the Bible says anything about the age of the earth or about the age of the stories written in it. Some scholars speculate the Hebrew "Bible" was collected into one source roughly 1,200 BCE, by the Judge Deborah during the time of the rule under 'Judges', or by Solomon in a time period not too distant from that. The 'New Testament; includes Paul's letters, starting the late 60s CE, other's writings through the end of the 2nd century CE. And all, of course, were modified repeatedly through the 400s and the exact 'books' included changed as recently as the 1,700s.