I'm turning 40 this week -- in style with a trip to New York with my wife and some friends. It will be a blast, and I'm really looking forward to the trip.
I remember when I was just out of college, and I was playing basketball with a regular group that was wide-ranging in age...but I don't remember anybody over 40. 35 seemed old then. Now, I'm still playing basketball regularly (4 days a week!), and 40 doesn't feel so old.
The way I look at it, I may be older than I've ever been before, but I'm also younger than I'll ever be again. :)