I'd strongly advise starting to play right handed if you can persevere with it. As you improve, the dreaded Mandolin Acquisition Syndrome will set in, and there is simply more choice for a right hander when looking for a decent mandolin. My daughter is left handed, and she is starting to play mando a bit (she's a hell of a pianist, but doesn't play fretted instruments.) I asked her about this just now, and her advice was the same; she says it doesn't really make a difference once the muscle memory is there. If you do decide to play lefty, I'd advise buying a decent quality lefty mandolin; it can cost serious money to swap a mandolin round, especially if you want a proper job doing on the nut, reversing and recompensating the bridge and possibly re-doing the top bracing. I've done a couple, and it's fiddly.
Tim