As I turn 40, I don't feel the angst I would have expected. Many cultures believe that happiness is not a constant state, but rather, it is an average, a summary, if you will. I've got a lot going for me right now: a considerate, supportive husband; healthy, thriving baby; enthusiastic friend network; close family; and creative inspiration (if not always the time to follow through).
Yes, there are some areas where I'd like to improve, such as taking off the pregnancy weight (39 pounds yet to go), but that's an achievable goal and, when taken into perspective, a minor concern. I'm still waiting for the all-clear from my doctor to get back in the pool, so I can resume water aerobics. When that happens, I expect to have better luck.
But overall, yes, I'm happy on this, the beginning of my 40th year.