After three years of classes, exams and internships, Brianna Taylor had a bachelor’s degree from the University of Nevada and was ready to put it to use. She had long dreamt of law school, but at 21 years old, she packed her bags and left her Las Vegas home for the one place she knew she wanted to be: Siberia.

“I took a step back and realized I wanted to travel. And law school wasn’t going anywhere,” she said.

For two months, Taylor lived in the tundra and taught English to Russian children. When fall arrived, she decided it was time to try someplace new. She packed up again and set out for Spain. Running low on cash, she went online and found a job as a nanny for a Madrid family.

“I needed a place to stay and I didn’t want to pay for it,” she said.

Taylor’s story is hardly unique among today’s crop of college graduates. Many now spend their 20s without stable employment, hopping from city to city with no end in sight. They sometimes struggle for years to find their way to adulthood, experiencing what is often called a “quarterlife crisis,” or QLC.

Coined in 2001, the term quickly found its way into pop culture. Quarterlife crises are the inspiration behind most of 25-year-old John Mayer’s music, the Tony Award-winning play “Avenue Q” and 29-year-old Zach Braff’s film “Garden State.” ABC is developing a series called “1/4life” which chronicles young adult angst. Even Britney Spears is wise to the concept, as the 23-year-old lamented in her 2002 song “I’m Not a Girl, Not Yet a Woman.”

But is this phenomenon really a crisis, or part of a larger, permanent shift in human development? Some experts say these seemingly aimless 20-somethings are not simply blowing off adult responsibility. Instead, they represent a new second phase of adolescence, extending beyond the late teens and into the mid- to late-20s. And in the process, they are redefining adulthood.

’30 is the new 20′

Alexandra Robbins, co-author of the book that launched the QLC craze, “Quarterlife Crisis: The Unique Challenges of Life in Your Twenties,” got to the heart of the matter in an interview on National Public Radio’s “The Diane Rehm Show” when she declared, “30 is the new 20.”

Indeed, more young people are postponing traditional adult benchmarks like marriage and parenthood until their 30s, using their 20s to explore careers, relationships and the world. This trend yields a new phase of life between ages 18 and 29, a gap between adolescence and adulthood that social scientists are just beginning to understand.

Dr. Jeffrey Arnett, a developmental psychologist at the University of Maryland, calls this phase “emerging adulthood,” which he says is a new stage of life.

Arnett describes it as a time of instability, self-focus and identity exploration. This developmental stage exists mostly in advanced industrialized countries and is usually confined to the affluent and college-educated.

His theory sparked a flurry of research since its publication in 2000. Emerging adulthood has since become such a hot topic in academia that the American Psychological Association now hosts an annual conference on the issue.

Time magazine recently created the term “twixters” to describe this group. University of Cambridge psychologist Terri Apter calls them “thresholders.” In England, they’re dubbed “kippers,” an acronym for “kids in parents’ pockets eroding retirement savings.”

Whichever term is used, the phase is hardly a passing fad. U.S. Census statistics reveal a decades-long trend toward delayed adulthood. In 1970, 64 percent of women 20 to 24 years old had married. That figure reversed by 2000, when 73 percent had never married. The census found a similar drop in marriage rates for 20- to 24-year-old men.

The delay in marriage can be attributed to many factors. Longer life expectancy and increased graduate school enrollment naturally makes married life less practical in the early 20s. Emerging adults were also raised in a world of changed gender roles, where women saw college as a chance for their own intellectual and career development, not a four-year husband-hunting expedition. Additionally, many of today’s emerging adults grew up with divorced parents, leaving them wary of jumping into marital bliss that might fizzle out.

Like marriage, parenthood is no longer the domain of the 20s. Women in their 20s account for a smaller share of all births, from two-thirds in 1980 to about half in 2002. The median age for first-time moms has crept up to 25 and first-time dads are typically almost 30.

Meanwhile, the birth rates for women in their 30s surged nearly 160 percent since 1976. Thanks to fertility drugs, birth rates for women in their 40s and 50s are also increasing dramatically.

Further evidence of emerging adulthood’s permanence is seen in society’s changing perceptions of being an adult. A 2003 survey found most Americans think people need to be 26 to be considered “grown up.” The survey was the first of its kind, but suggests society’s notions of adulthood have aged since the Baby Boom, when 18-year-olds were considered old enough for marriage and parenthood.

The in-between years

Dr. Arnett described the attitude shift in his 2004 book “Emerging Adulthood: The Winding Road From the Late Teens Through the Twenties.” Due to increased standards of living, emerging adults expect more out of life and are taking more time to explore their options, Arnett explained.

The unpredictability of this lifestyle often leaves young people feeling “in-between” as they struggle to balance adolescence with adulthood, according to Arnett. While some revel in the spontaneity, it can be a purgatory for those who lose personal connections.

Brianna Taylor did not know anyone when she arrived in Spain and had to find her own way. She joined a local English-speaking church to make friends. “In college, your community is handed to you on a silver platter,” she said. “Once you graduate, you have to work a little harder to find your community, but it’s out there.”

Although many in their 20s feel they need to take time off to assess their priorities, some simply don’t want to feel trapped.

“I don’t want my quarterlife crisis to end,” said junior Kelly Cogswell. “I’d rather be in-between than in a cubicle job I hate or married and having some jerk’s babies.”

Some might dismiss such attitudes as reckless or hedonistic, but Taylor thinks her emerging adult wanderings were worth it. “Traveling and being abroad gives you a bigger picture of the world. It gives you confidence in your abilities,” she said.

Far from the Siberian plain, Taylor now works for the governor of Kentucky, making phone calls from an earpiece and checking her e-mail on a BlackBerry.

“It’s a weird life because you still identify with college, but then you’re sitting in meetings with 40-year-olds and they consider you their equal. It’s definitely something you have to step up to,” she said. “Thankfully there’s a whole generation of people going through the same thing.”