All the way back to Origen, theologians were not sure that the world was necessarily created literally as it is in Creation. St Augustine assumed the world was created instantly, other theologians thought that perhaps each day of the 6, represented 1000 years (due to a NT verse). Now, they did generally assume that the world began in ~4000BC, but they weren't completely wedded to the idea (if each day represents 1000 years, some suggested, perhaps the world was created in ~10000BC). The key thing they were really keen on was that the world wasn't infinitely old, as some pagan philosophers suggested. Now, the Protestant reformation led to the increased influence of Martin Luther as a theologian, who did believe in the literal truth of the Creation story. It's only in the 19th century, with ideas like evolution and the improvements in paleontology, that the idea that the world was older than a literal reading of Genesis suggests, became widespread (though it was resisted by conservative Protestant theologians: I don't know about Catholic theologians, as my knowledge of 19th century religion is largely Anglo-centric. I'd be keen on finding out though, if anyone else knows!). I can't tell you the exact details of that process though, maybe someone else can.