What is it about the 20 somethings?

He was teaching human development and family studies at the University of Missouri, studying college-age students, both at the university and in the community around Columbia, Montana.

He asked them questions about their lives and their expectations like, “Do you feel you have reached adulthood?”

“I was in my early- to mid-30s myself, and I remember thinking, they’re not a thing like me,” Arnett told me when we met last spring in Worcester.

“I realised that there was something special going on.” The young people he spoke to weren’t experiencing the upending physical changes that accompany adolescence, but as an age cohort they did seem to have a psychological makeup different from that of people just a little bit younger or a little bit older.

This was not how most psychologists were thinking about development at the time, when the eight-stage model of the psychologist Erik Erikson was in vogue.

Erikson, one of the first to focus on psychological development past childhood, divided adulthood into three stages — young (roughly ages 20 to 45), middle (about ages 45 to 65) and late (all the rest) — and defined them by the challenges that individuals in a particular stage encounter and must resolve before moving on to the next stage.

In young adulthood, according to his model, the primary psychological challenge is “intimacy versus isolation,” by which Erikson meant deciding whether to commit to a lifelong intimate relationship and choosing the person to commit to.

But Arnett said “young adulthood” was too broad a term to apply to a 25-year span that included both him and his college students.

The 20s are something different from the 30s and 40s, he remembered thinking. And while he agreed that the struggle for intimacy was one task of this period, he said there were other critical tasks as well.

Arnett spent time at Northwestern University and the University of Chicago before moving to the University of Missouri in 1992, beginning his study of young men and women in the college town of Columbia, gradually broadening his sample to include New Orleans, Los Angeles and San Francisco.
He deliberately included working-class young people as well as those who were well off, those who had never gone to college as well as those who were still in school, those who were supporting themselves as well as those whose bills were being paid by their parents.

A little more than half of his sample was white, 18 per cent African-American, 16 per cent Asian-American and 14 per cent Latino.