I found this article interesting: http://www.economist.com/node/17722567
Self-reported well-being follows a U curve. "Happiness" declines starting at age 18 and keeps going down until it bottoms out in middle-age. But then, interestingly, it rises, and keeps rising, all the way to end of life. This has been observed all over the world.
What's the global average least-happy age? 46.