Board Thread:Character Discussion/@comment-24279891-20140506075618/@comment-15736398-20140514173007

Emma, Snow, and Charming all repeatedly referred to them all being the same age throughout the early portion of Season 2 (as did Adam and Eddy), but we did see Snow's birthday in The Queen is Dead, meaning that she's now either 29 or 30 in Season 3 (depending on whether or not she's had another birthday since the events of  TQiD); we also know that Emma is now 29 thanks to the reference in The Tower about it being 'almost' 30 years since Emma's birth.

If I were going to hazard a guess, I'd say that Emma and Snow are both 29 as of the end of Season 3, with Charming also possibly being 29 depending on when his birthday is.