I just read this article in the Atlantic. I'm 49 and I haven't felt right for about four years now. I wouldn't say I feel extremely depressed, but I definitely have the 'is this all there is to life' funk going on.
I haven't died my hair, bought a sportscar, got a mistress, etc... I just want to be happy again, and according to the article it is coming in my 50s.
http://www.theatlantic.com/magazine/archive/2014/12/the-real-roots-of-midlife-crisis/382235/