“Until very recently, we had to make some pretty important life decisions about education and career paths, who to marry and whether to go into the military at a time when parts of our brains weren’t optimal yet,” says neuroscientist Jay Giedd at the National Institute of Mental Health, whose brain-imaging studies of thousands of young people have yielded many of the new insights. Postponing those decisions makes sense biologically, he says. “It’s a good thing that the 20s are becoming a time for self-discovery.”

Delayed Development: 20-Somethings Blame the Brain - WSJ.com