When I drifted into my 30's, I noticed that everything seemed to give me indigestion. I'm 43 now, and I haven't noticed any other significant changes. I know they are coming, tho.

I'm fortunate in that I've yet to get any lines or wrinkles on my face, not even crows feet when I smile. I also have very light blonde hair, so the white that's coming in just looks like highlights.
Psychologically, I'd say changes began in my mid-30's. Thoughts of sky-diving lessons and the like have been pushed aside. The older you get, the more you realize the risks of certain things.