The rabid anti-evolutionary school of religious thought that most people picture when they think of creationism is actually a recent and radical subset called Young Earth Creationism. Based on a long-standing fringe theory about the Earth being merely a few thousand years old, the idea of a "young Earth" was popularized in the early 20th century by a man called George McCready Price, a Canadian wannabe geologist and anti-evolutionist who made up for his total lack of scientific training with an unbridled enthusiasm for ignorance. Seriously, he was proud of the fact that he never caught "the disease of Universityitis."
Even in ancient times, Christian scholars didn't buy that bunk. Take St. Augustine of Hippo, who was extremely clear that no one should view the Book of Genesis as a documentary. St. Augustine, it should be mentioned, lived in the 5th century. For centuries, it was understood that the Genesis was an allegory: The "days" of creation weren't actual 24-hour periods, but metaphors for a really long time, which in the eyes of an eternal, omnipotent, time-transcendent God just seemed like an average work week. That's not just the stance of one surprisingly progressive Hippo; this very view was and remains the Vatican's (and therefore the Catholic Church's) official stance on the subject.