Why are these errors in the Bible, supposedly the perfect word of god?

A lot of people agree that most if not all of Genesis is fake, even Christians. Some Christians take it literally. Most Christians try to reconcile errors in the Bible with inaccuracy on the part of the writer's interpretation, as well as cultural differences. For example, I've heard someone say once that Moses being 900 could be explained by the use of a different calendar, probably one based on cycles of the moon (So a little less then a month was a year)