Why does America have such a generation glut?

Longer life spans are part of the explanation. But a bigger reason is the eagerness of demographers and sociologist to slice and dice the marketplace into thinner and more precise segments.

There are distinct differences between even the two youngest generations, demographers say.

Generation Y, born after 1977 - also called Echo Boomers, the Digital Generation, or Millennials ­ are "the biggest population bulge since the Baby Boomers," says Maddy Kent Dychtwald of Age Wave LLC, a generational research firm in Emeryville, Calif. "Having grown up in the best overall economy ever, they are materialistic, optimistic and affluent."

'Self-esteem on steroids'

Raised in an era where parenting "came back in style," they got loads of encouragement and support and have been described as having "self-esteem on steroids," says Fishman.

Generation X, born between 1965 and 1977, is a smaller and far more cynical group, says Dychtwald. "They don't like to be identified as a group. In fact, they don't like groups in general. They are more cautious and pessimistic than their younger brothers and sisters."

Gen-Xers were the latchkey kids who grew up in an age of divorce and two working parents and who entered the workplace during a recession. Xers "believe older generations have made a mess of things," says Fishman.

"The program Friends is just one example of how this generation has substituted friends for where family has failed," she observes.

Meanwhile, in a survey last year, Gen-Yers "chose their parents as their heroes," says Dychtwald.

Of course, it is a gross simplification to try to assign personality traits to a generation.

"It's a Cliff Notes way of explaining things," says Thompson, the popular culture expert. "But we tend to define the entire generation on images attached to a small group within it."

While sometimes called the "Woodstock Generation," not many Baby Boomers were actually at Woodstock or even devotees of the lifestyle that the concert connotes, Thompson explains.

But because "generations" are so much a part of the popular culture, many Americans identify with their age cohort. Some even shape their self-perception to fit the generational image.