Science adjusts it's beliefs based on what's observed
Faith is the denial of observation so that Belief can be preserved.

Are there really people who think that the universe is 6,000 years old and was created in 7 days and so on...

Been watching the Bill Nye / Ken Ham debate and I'm still not convinced that they're not just having a laugh.

Are people seriously so stupid? (It might be insulting to call them stupid but there really is no other word that will do).

There are counties and states in America, where Creationism is taught in schools as a science and evolution is a heretical belief that is illegal and cannot be discussed, let alone taught in school.

Christians believe the world was created in six days.

Some do, some don’t. The majority that do are fundamentalists or “born again” - the lot who basically came from the Puritans. They take a literal reading of the Bible, and believe that what’s in it is 100% rue - even the bits that contradict others. There are other Christians - mostly CofE and Catholics - who take a differing view - not everything in the Bible is a 100% accurate transcript of what happens, it’s a series of stories, parables and analogies. The world didn’t take literally six days to make, but it’s way of expressing a period of time. What’s a day to a God anyway? Who knows what a deity has as a timescale? It’s more likely that it’s a good excuse to say that after six days of hard work you’ve earned a rest.