A couple of economists have studied happiness levels Europe and the U.S. Specifically, they surveyed relative happiness versus age. They find that the same people report that they are pretty happy in early adulthood, but that happiness generally falls afterwards, reaching its lowest levels by age 45, before then increasing in old age. This trend is as strong as the effect of wealth on happiness.
In the United States, the steady decline in happiness from age 16 to age 45 has an effect that’s larger than a 50 percent reduction in income. And, equivalently, the 15-year upswing in happiness that follows age 45 is stronger than the upswing that tracks doubling of income.
The studies also found that Americans have steadily become less happy during this century. Baby boom men born in the 1960s are less happy than those born in the 1920s. (Presumably after correcting for age). The effect is as much as being 10 times poorer.