Growing up isn't what it used to be. There's a yawning gap between the end of adolescence and the beginning of adulthood: a period when millions of 20-somethings and 30-somethings have many adult freedoms without all the responsibilities. Social scientists have tried — so far in vain — to name this new life stage, but no one should question its significance.

If you have doubts, a new U.S. Census Bureau study should resolve them. It compares the experiences of Americans 18 to 34 now with the same age group in the 1970s. There has been a sea change. "In prior generations, young adults were expected to have finished school, found a job and set up their own household during their 20s — most often with their spouse and with a child soon to follow," says the report.

No more. If adulthood ever equated with marrying and settling down, it doesn't now, the Census Bureau says. Asked in opinion surveys about what defines becoming an adult, Americans cite finishing schooling (61.5 percent "extremely important," 33.3 percent "somewhat important") and having a full-time job (51.5 percent and 43.1 percent). Getting married (11.5 percent extremely important, 33.9 percent somewhat important) and having a child (10.4 percent and 34.6 percent) are way down the list.