first you have to accept that dragons have the possibility of having been real. All tetrapods have 4 limbs, and evolution has resulted in some flying animals (bats, pterosaurs, birds, to be exact) with the gradual modification of the forelimbs into usable wings, and other adaptations that enable them to fly, such as hollow bones and the like. So even if dragons were real, they would not have forelimbs, but instead have wings and hind legs. Another thing to consider is that all the idead of mythical dragons I have seen don't seem to have the ideal bodies for flight. Simply having wings doesn't guarantee it will be able to fly well, numerous adaptations must exist as well.