Aging brings wrinkles, sagging bodies and frustrating forgetfulness. But getting older is not all bad for many people. Mounting evidence suggests aging may be a key to happiness. There is conflicting research on the subject, however, and experts say it may all boil down to this: Attitude is everything.

In one study, the average number of years a 30-year-old in the United States could expect to live increased 5.4 years for men and 3.6 years for women between 1970 and 2000. During that same time period, men gained 6.8 years of happy life and shed 1.4 unhappy years. Women chalked up 1.3 happy years, but the number of unhappy years didn't change for them, according to research published in 2008 by Yang Yang, a sociologist at the University of Chicago.

Aging can bring more cheer as people become more comfortable with themselves and their role in society, according to another study published in 1989 by Walter R. Gove, professor of sociology, emeritus, at Vanderbilt University in Tennessee.

Happiness in old age could come down to how one stacks up to same-age peers or one's own expectations – say you're used to breakfast on a silver platter and when you get older you can only afford the basic English muffin. It turns out, individuals who adapt the best to changes also have the highest expected levels of happiness, according to the Population Reference Bureau.

Despite the conflicting findings about aging and happiness, the good news is that there doesn't appear to be a limit to how much happiness one can achieve in one's life.

"Most people desire happiness but no one has identified a limit to attainable happiness."