At first I also got the impression that Yoruichi was a lot older than Soifon, but now I think their age difference could be almost anything, really. I liked the story, but I think I would have had the same reaction as Soifon at hearing that, hehe. And I hope she doesn't think she only got where she is because Yoruichi wanted her to, and not for her own merit.
Anyway, very nice story, I really enjoyed reading. Hope you update your fics soon, I like them a lot too.