World wide research consistently shows that people get happier as they get older. This is called the "U bend of happiness" effect and it has been well documented in many university studies. 

Social economists from the University of Melbourne have recently confirmed the age-old suspicion of a dip in human happiness during middle age. It seems that the lowest point occurs in people's 40's (perhaps prompting the typical "mid life crisis"?) and then things just keep improving from there.

"We have identified a clear 'U-shape' in human wellbeing," says researcher Dr Terence Cheng, from the University of Melbourne's Institute of Applied Economic and Social Research. He says past evidence for "mid-life crises" have come from cross sectional data. That is, by comparing surveys of different people’s happiness at different ages. But now, for the first time, researchers have tracked the happiness levels of thousands of people across three countries over multiple decades.

The Economist magazine has also documented research on the "U bend of happiness" with an interesting article containing commentary and links to various research on the subject.

University of Melbourne Insitute of Applied Economic and Social Research.

The Economist article on age and happiness: The U Bend of Happiness.