the original poster said he did not want to go as low as 30 because then she would have known he was patronizing.
If for some reason you have to guess, play the game and say 30 even if you think it sounds patronizing. It's the standard, expected little white lie, along the same lines as "Fat? In that dress? Hell no, you look fantastic."
The best advice so far was from the guy who said not to even play the age guessing game.
Yes.