I've wondered how old Holly's supposed to be. She's usually portrayed as very young, but looking at the overall timeline... She was 13 in Batman: Year One. Dick was 26 around [i]Infinite Crisis.[/i] Add OYL and the time that's passed in the books, since, he's gotta be at least 28, now. He's now supposed to have been 16 when he became Robin. So, how old Bruce, Selina, and Holly are depends on when Dick became Robin (It used to be during Year 3, but who knows, now?). In Year 1, Bruce was 25. Brubaker's run established Selina as 17 and Holly 13, at that time.
Dick keeps getting older when he debuted as Robin. He was 8 from the Golden Age through the Bronze Age, 12 in the immediate post-CoiE continuity, and now 16. That's the problem when you have this one character aging and maturing... They have to account for everybody else. So, they have to make him older when he started to shave some years off of Bruce and Selina. :)
But, if he bacame Robin during Year 2, Selina is now around 30, if Year 3 around 31. So, that little incident where she was messing with Dick wasn't really robbing the cradle, since she's only two or three years older than him. This puts Holly at about 26 or 27, now.