The answer is he was born during B.C. not A.D., or as failure had said ( for some reason that movie always pops into my head whenever I think of weird stuff like this, that movie is creepy). I really hope you didn't make your own stupid answer up like "o he used a time machine to get his past self and bring his past self who was 15 to the present when he was 20" because that would be illogical and dumb.