The boundaries between Generation Y and Generation X are fuzzy. Some researchers define Gen Y as those born between 1978 and 2000.

Others put them firmly among the "9/11" generation, born between 1982 and 2005.

Minimum estimates put Gen Y at 75 million strong. That’s twice as big as Generation X, and almost as large as the Baby Boomers, the first generation born after World War II.

Experts say generational shifts occur about every 20 years.

"Generations are composed of people who were about the same age when they experienced the big events of their time and have come to share attitudes and dispositions that are influenced by them," University of Kansas associate professor of communications Tracy Russo said in an e-mail to Stars and Stripes.

Life-shaping events frequently cited for Gen Y, also known as "the millennials," include the breakup of the Soviet Union, the spread of AIDS, the O.J. Simpson trial, Monica Lewinsky, the Columbine High School massacre, the Oklahoma City bombing, the development of the Internet, the Dot.com boom and bust, the advent of reality TV, and the 9/11 terrorist attacks, according to Russo.

Beyond these big events, generations share culture, Russo said. For Gen Y, cultural icons include Michael Jordan, Princess Diana and Bill Gates.

The millennials grew up with Beanie Babies and Barney, virtual pets, the X Games, the Spice Girls and hip-hop.

Their brains are hardwired for multitasking, a product of being part of the digital age, said P.W. Singer, a senior fellow at the Brookings Institute, a Washington think tank.

He cites one study that found Gen Y’ers spend on average 6.5 hours a day using digital devices but packed 8.5 hours of usage into that time, talking on a cell phone while on the computer or playing a video game, for example.

"Gen Y has always had computers, and they call on electronic connectedness to confirm their identities," Russo said.

Staff Sgt. Roderick Jefferson, 25, of the 35th Communications Squadron at Misawa Air Base, Japan, said the Internet and its world reach has made his generation more team oriented.

"We look at, ‘How is this going to affect everyone rather than how is this going to affect just me?’ " he said.

Based on observations of her college students, Russo sees millennials as being "very much wanted" by their parents, as well as sheltered and protected. She compares growing up as a Boomer and being told to come home when it gets dark to her grandchildren today who don’t stray far alone and whose play is often supervised.

Many millennials had or have "helicopter parents" who hover, Russo said.

"These parents organize everything … make everything right," she said.

Gen Y’ers are also conventional and confident, Russo said. They "want to do things right. It’s how they were rewarded by their hovering parents," she said.

Confidence is a result of being rewarded consistently since childhood, she said.

"Think soccer teams that never made a goal but where all the kids got a trophy," Russo said.

And Gen Y is also the first generation "that actually likes their parents," Singer said, a result of parents who wanted to be their best friends growing up.

In surveys when millennials were asked who they most admire in the world, he said, "this is the first time that Mom and Dad came in first place."