A study to be published in the July issue of the journal Child Development reports that a constellation of pseudo-mature behaviors in early adolescence — minor forms of delinquency, early romantic behavior and a focus on physical appearance in seeking out friends — predicts “significant difficulties in social functioning” up to 10 years later. Individuals who act “old” for their age as young teenagers tend to have trouble forming friendships and romantic attachments as young adults. Why would this be? Joseph Allen, a professor of psychology at the University...