Hmm…well, I can’t really speak to individual psychology, because the personal reasons someone finds something erotic is pretty hard to pin down. What I can discuss is how the aspects of the rebel-to-stodgy TF fit in with various fetishes, and that might help clarify a little bit.
So, the specific details in a Rebel-to-Stodgy or (R-to-S) TF line up best with age progression, I think, and the two share quite a bit in common. Part of the appeal of AP, one of it’s erotic triggers if you will, is that growing older cuts the aging character off from possible lives. By aging, it’s no longer possible for that person to do certain things or be certain types of people–losing that control is part of the eroticism of AP, especially extreme variations, into middle age and beyond. (Sidebar: AP into ages younger than this is different, actually, especially if the character starts as a teenager or younger. There, growing older, into one’s 20’s or 30’s is seen as a burgeoning of possibilities, not a restricting of one’s possible lives.) The R-to-S has that same sort of feeling–that control has been ripped from the character, and that their life is now predetermined, but in one way it’s even more extreme, because AP skips ahead, while R-to-S forces the person to live every moment of their now calcified life.
In addition, there are a few similarities R-to-S has with forced-into-slavery narratives. They both involve forcing someone into a societal role which is alien to them, requires them conforming to extreme social rules and standards of dress and behavior, generally in a submissive role. It’s just that instead of leather, rubber, shaving, and body modification, the tools of slavery in R-to-S are three piece suits, cigars and pipes, and dinner manners. Still, the underlying format and eroticism is the same, believe it or not. So, if that turned you on and you weren’t quite sure why, it’s probably one of these two similarities.