Well, I recently had a birthday and turned 50. I normally have a crisis every 10 years on the birthdays ending with zero. When I turned 20 I was depressed because I wanted to have a baby. That happened when I was 24. Then when I turned 30 I was depressed because I never finished my BA degree, that happened when I turned 38. Then when I turned 40 I guess I was depressed because it had become a tradition with me by then(actually I can't remember exactly why I was depressed, but I think it was the whole now I'm middle aged thing). So you might ask, what was I depressed about this birthday? And the answer is NOTHING!
Oh, my life isn't perfect and I could have probably made myself depressed if I had dwelled on all the things in my life I am not exactly thrilled about, for example I live in a renovated 2 car garage for heavens sake, my hair is completely gray(all of it), my boobs and my belly button are best friends now because they hang around with each other so much and I often feel grateful that MOST of the teeth in my mouth are still mine. BUT I am also old enough to know that we don't live forever, and we don't know what the future hold. So I decided I wasn't going to waste a day that I could spend loving my family and being happy, by worrying about stuff I have no control over(like gravity). I also feel 50 is old and young enough to be a grandparent, which is the most important thing in my life these days.
So in short, I had a nice birthday, it was spent with family and that is all that matters!