I have a cyan N9 from October 2011. It looks fine as on the first day except for some dents around the battery flap, and the coating came off completely off the flap (but only of the flap). Once the coating came off the flap completely, it looks as new again, and you'd notice no difference, but it became more susceptible to minor scratches, so you can see some scratches on it now.
But the unibody is still fine as on day 1. The camera chrome has some scratches, but that begin on day 1 already, so it's not a sign of age.