Youth mental disorder diagnosis chartUp to half of U.S. children and adolescents meet diagnostic criteria for at least one mental disorders by age 18, according to the first nationally representative, face-to-face survey on the topic. The data, released in October by researchers at the National Institutes of Health, also showed that many of these disorders emerge early — with an average age-of-onset of 6 for anxiety disorders, 11 for behavior disorders, 13 for mood disorders and 15 for substance use disorders.