Really, 30 is the new 20? Forget that series Netflix (NFLX) is reviving -- this is arrested development.

Jeffrey Arnett, a research professor in the psychology department at Clark University in Worcester, Mass., and the author of "When Will My Grown-Up Kid Grow Up? Loving and Understanding Your Emerging Adult," has devised a theory that considers the period from 18 to 30 a "new life stage between adolescence and young adulthood."

Arnett posits that 20 was the accepted age for hitting adulthood 50 years ago, but folks around that age today are just starting to sort out their careers and lives and are putting off marriage and children until after 30.

That line of thinking has already sparked a mini backlash among folks like Susan Patton, the mother of a Princeton University student who advised the school's female students to find a husband before graduating. It was also the topic of a long thesis by Newsweek writer Megan McArdle, who warned that families may not get the number of children they want if they wait until they're financially and socially stable before having them.

Woman holding empty purse (© image100-Corbis)
McArdle notes that college grads who wait until they're 30 or older to get married report an average annual income of $50,000 --  $20,000 a year more than those who marry before 21. That dovetails nicely with Arnett's observations about couples living together longer before getting married, planning for fewer children and developing full careers before starting families.

Does that make the millennials whom Arnett observed lazy or selfish? He says they just have really high expectations of both life and their jobs and are willing to do what it takes to get to those fulfilling gigs later. If that means working for minimum wage, as 284,000 college grads are doing, or making less money doing time at Starbucks (SBUX) or Wal-Mart (WMT) in exchange for college credits, they're in.

And selfish? This is a generation that's shunning Wall Street and that considers a position at St. Jude's Children's Hospital an ideal gig. Maybe their baby boomer parents instilled an oversize sense of confidence in them, but nine out of 10 of these "emerging adults" told Arnett they agreed with the statement "I am confident that I will eventually get what I want out of life."

If they're willing to ride out their 20s in low-paying jobs to ensure a gig at St. Jude's or Google (GOOG) in the future and somehow haven't had their dreams ground into dust by age 30, maybe Arnett is on to something. Maybe development occasionally needs arresting.

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