Fraught with hormonal imbalances, parental meddling and confusion about what comes next, adolescence is often dismissed as a best-forgotten prelude to the eternal joys of adult responsibilities.

But if adulthood is so great, why are so many young and not-so young people putting it off? In many societies, men and women in their 20s and beyond are delaying marriage, career commitments and even leaving their parents’ houses. The shift is pronounced enough that social scientists are struggling to define a whole new life phase with names like “delayed adolescence,” “emerging adulthood” and “the odyssey years.”

By any name, it describes a time of restless experimentation and shiftless wandering. As David Brooks wrote in The Times, “During this decade, 20-somethings go to school and take breaks from school. They live with friends and they live at home. They fall in and out of love. They try one career after another.”

Despite Hollywood’s growing subgenre of comedies about clueless man-boys, the new 20-somethings are not all unmotivated slackers. As Mr. Brooks adds, many young adults around the world are responding to cultural upheavals brought on by the shift into an information-based global economy.

Good jobs are harder to find, less secure and require more education, making settling down less of an option. Robin Marantz Henig wrote in The Times Magazine that “despite elements that are exciting, even exhilarating, about being this age, there is a downside, too: dread, frustration, uncertainty, a sense of not quite understanding the rules of the game.

Directionless 20-somethings ? and their prematurely gray parents ? may find some solace in neuroscience. As The Times reported, it was long believed that the brain reached maturity at puberty. Recent studies, however, suggest that it takes until age 25, at least. In particular, the prefrontal cortex and cerebellum, responsible for emotional control and cognitive function, tend to lag in their development.

So a few extra years of rootless confusion may be just what nature intended. Anxious parents can at least keep a n eye on their adult children, as many are living at home. The global recession has made affording an apartment, much less setting up a new family in a house, seem insurmountable . In America, 40 percent of people in their 20s move back with their parents at least once, The Times reported. In Italy, staying home with Mom goes beyond economics. The “mamoni,” or mother’s boys, are blamed for the country’s chronically low birth rate.

With a mother to cook and clean through adulthood, who needs marriage? And in India, even married and successful men consult daily with their mothers. “There is a huge, continuing umbilical cord between mothers and sons,” Tarun Das, a commerce specialist in India, told The Times. This trend probably isn’t new. N or are “emerging adulthood,” “delayed adolescence” or “the odyssey years.”

As The Times Magazine reported, in 1970, Kenneth Keniston, a Yale psychologist, published a report on the rootless, confused lives of the young people of that era. “Postadolescents,” he wrote, were unable to define “questions of vocation, questions of social role and lifestyle.” In other words, he wrote, they just “can’t seem to ‘settle down.’ ” His own label for this stage of life? “Youth.”

KEVIN DELANEY