Not so much a theory as clearing up a small point. In The Great Hunt (Chapter 28) the Aiel Urien says to Verin, "Wise One, my water is yours." Verin asks him why he calls her that and his response is, "No, Wise One. But you have the look of those who have made the journey to Rhuidean and survived. The years do not touch the Wise Ones in the same way as other women, or as they touch men."
I felt it needed clearing up as some posts are overlooking this one piece of info when talking about Aes Sedai and the Oath Rod being the reason for their youthful appearance.
wotmania says: Good point. Hmmmm... Perhaps the Oath Rod just shortens the lives of those who swear the Three Oaths. But I still wonder why the Forsaken do not have the ageless look.
Comments
Just because the Aiel said that the years did not touch Verin as they did not touch the Wise Ones (speaking of which he made it sound like all Wise Ones, but not all Wise ones can channel so maybe something else) but anyways back to the point. Maybe he just meant that verin did not look as old as some other clues besides her face would point to. Everybody seems to assume that slowing and agelessness are the same thing but for the most part we can never be sure if the person is talking about looking youthful and looking ageless.
They get many advantages from being a "chosen." One of these must be that they do not need the ageless look, just as they are immortal. They are connected to the darkn one after all.
The "Kin" are also able to channel and do not have the "agelessness" about them. And don't forget, some of the Kin are over three hundred years old. Since that is true, it doesn't necessarily follow that the lack of agelessness is a gift from the DO. Since only the AS seem to have the ageless faces, it must have something to do with the way they use the one power that is different from the other channelers. If it is not the oath rod, then it could be the way they handle the flows.
Maybe the great serpent ring they have is some odd ter'angreal that makes them have the agless look....
Throughout these theories posted so far, two examples of why the oath rod cannot be the cause of the agelessness have been mentioned and two haven't yet come up. One is the accepted that is 80 but looks 20. Another is the comment to Verin about having the look of a wise one. What do the two have in commen? Both have been through a version of the Accepted test; the three rings.
The two points that haven't come up is that One: our girls, Egwene, Elayne, etc, that haven't yet taken oaths but HAVE performed the ritual of the Accepted, are starting the show signs of agelessness; and Two: Cadsuane and the older Kin both are ancient and show signs of age and these people have also taken the Accepted ritual in many cases. Perhaps after so many years, the agelessness simply becomes less aged. I mean, really, what does agelessness mean? Perhaps it is simply that one has the face of a young woman and the eyes of an old one?
I think Eggy said it pretty straight...maybe he/she needs to post this as a theory.
i think eggtooth brought up a very valid point, but in addition, maybe the ring ter'angreal the wise ones must go through in rhuidean has some sort of effect on ones' appearance of age. also, i get the impressions that none of the Kin have the exact same agelessness as aes sedai, or elayne and nynaeve woulg have noticed and made a point of factoring it into their decision that the oath rod must be the reason. perhaps it is a combination of effects from the rings or some other device that is used for the tests from accepted to aes sedai that give the women the agelessness. jordan hasn't really explained much of that set of tests beyond that the oath rod is involved. i cant imagine it is just a matter of swearing on the oath rod. i dont think we have seen enough about these tests nor have we seen enough descriptions of wise ones' appearances to really make any theories that cant be picked apart easily. theres no telling how the uses of all these ter'angreal affect women (and men) differently.
oh, and dont forget about other women who have been using the power a long time (wilders, windfinders, damane, suldam?)
too early to find a solution that we can even pencil in, but it is still fun to try

onnestabe
the wise ones, the kin, and the aes sedai all slow. this comes from long use of the one power. but only aes sedai have the ageless face. this is from using the oath rod. on of the forsaken say that they bind themselfs like criminals. then later says that they gave her a choice to be bound from her pleasures (hurting people when she would Heal them) marked and see the end of her life coming. this marking could be the ageless face. it also explanes why aes sedai do not like as long as the kin.
Thinking of things for sig's is hard
Could mean