This makes me think about a book I read a year or so ago called The Happiness Curve by Jonathan Rauch.

The idea is that happiness peaks in your 20s when you have great expectations and infinite possible outcomes for your life. As you age, you make choices, and reality sets in, and it inevitably leads to some amount of disappointment and dissatisfaction with life.

Fortunately, the happiness curve tends to trend back upward starting around age 50. The author's explanation for this is that happiness is based at least partially on your expectations. The idea being that your expectations are finally adjusted downward enough by the time you reach your 50s that you can be satisfied with normal life.