As Goodison_Lad said, they are both aging slowly in the other one's rest frame. (In A's frame, B is aging slower. In B's frame, A is aging slower). There's no contradiction here, because of what I said in my previous post. If one of them turns around so that they eventually meet again, the one who turned around will be younger. This result can't be calculated with the time dilation formula alone, because there are at least three inertial frames involved.