If dragons (and sea monsters) were dinosaurs how does that prove creationism?

I'm not asking for an argument one way or another, I want to understand the logic that links dinosaurs living after the cretaceous(?) and after the last ice age, with conclusive proof of a young earth. For the record, I'm a Christian, so I believe in creation, but I also believe in evolution and I don't see a conflict. So like I said I'm not interested in either an evolution vs. creation answer or vice versa. Here's the issue: I understand that young earth creationism might require dinosaurs to have been around past the ice age (to explain fossils or whatever). But if we concede the possibility that they were, does that automatically prove young earth? It shouldn't, right? Don't most people vaguely suppose that the Loch Ness monster and possibly dragons were some sort of rare hangover from the cretaceous anyway? Can't you believe that without denying evolutionary theory (including old earth) as generally true?