Siuan and Leane were both very young for channelers, even oathbound ones. I suspect that the change in their appearence had far more to do with the loss of the ageless look rather than age reversion.

The big test will come when someone as old as Cadsuane with gray hair, wrinkled skin and internal organs decayed from age removes the oaths. It just feels a bit silly that someone like that would just *POOF* turn into a young woman like that. I think it would be far more powerfull if the AS really had to choose between the oaths and longer lives.

Does Rand say anything about the oaths or the binder to anyone? I presume he would know thanks to LTT.