Throughout my life I have always dressed younger then my real age. But then again, I don't look my age so I think it's perfectly fine. I have come to the conclusion that I don't follow direction well. :)
Because of this, I think it's fine to dress anyway you want at ANY age...within reason of course. If you can pull it off, DO IT! If you like to follow direction, Who What Wear has a great piece today on things to think about when one contemplates their age and attire.
Here are some of my favs: Leigh Lezark (29):
Olivia Polermo (almost 28):
Rachel Bilson (32):