Just because a religion is still practiced doesn't mean it can't be considered a mythology. I said it in a previous post, but the word "myth" derives from a Greek word that means "Speech with God(s)". The word is used incorrectly, pretty much. Mythology is a study of religions when it comes down to it, so Christianity is indeed included in that rather some may wish to deny it or not.
As far as Mythology and the Bible are concerned, not counting actual history, there is (so far) not a single story in the bible that cannot be traced to other older religions. What Christians consider Mythology.
Not true. Have you heard of the historical Jesus? Historical Moses? Historical Noah? There's very convincing facts that prove that they may have existed. (There's even a book out there saying Jesus was just a politician and faked his own death. Because who wouldn't believe the words of someone who died, and came back to life?) True, some things may have been exagerated to make the situations seem more miraculous (their ages for one) but that doesn't mean it couldn't have happened.
Also, Noah's Ark seems to be a direct copy of a man Gilgamesh encounters to be able to gain immortality. He basically builds a ship and brings his family aboard (only he knew about the flood that occurs). They are then spared from drowning like everyone else (everyone was meant to die, but a god told the man ahead of time what was going to happen) and so him and his family gain immortality.
Also how about..dragons for instance? St. Michael and St. Margaret led angels to kill dragons. Dragons seems to be in almost every culture in some form or another. Maybe this is what led to the extinction of dragons, if they did exist. (I personally believe they did. If creatures like dinosaurs can exist, then why not?)
Sometimes I think people attack Christianity way too much, yes it is a young religion but it also stems from Judaism and Muslim as you said.