Many say that Christianity was started by Jesus Christ in Judea, so the date would be about 30 AD. But the writings in the Old Testament point to the coming of the Messiah (the Christ): Isaiah around 700 BC prophesied about the Messiah, see Isaiah 52:13-53:12 "See, my servant, will act wisely; he will be raised and lifted up and highly exalted. Just as there were many who were appalled at him – his appearance was so disfigured beyond that of any human being and his form marred beyond human likeness – so he will sprinkle many nations..." Even right at the beginning of the Bible the Messiah is prophesied, see Genesis 3:15 "...he will crush your (Satan's) head, and you will strike his (the Messiah's) heel." Therefore you can say that Christianity is over 6000 years old.