I was surprised to learn that the concept of a mid-life crisis has surprising amounts of research and data behind it. Happiness falls from one's early 20s to mid / late 40s. Then, it rises again and keeps rising until the body or mind breaks down just prior to death. In fact, happiness is higher late in life than levels even experienced in youth. Further, this finding seems to be a fairly robust across generations, socio-economic status, countries, and even across species!
Happiness is often described as the gap between reality and expectations. An interesting hypothesis is that our gap between reality and our expectations grows during our 30s and 40s but that in later years, wisdom allows us to better appreciate reality while simultaneously have more meaningful control of our expectations. If happiness = reality - expectations, then wisdom is about how to measure those two variables better.
There is more here.
