Seventy-five percent of mental disorders manifest themselves by age 24, but fewer than 1 in 5 young people were treated for such disorders, a panel of mental health experts said at a Senate hearing on Thursday. In response to the Newtown, Conn., school shooting, President Barack Obama has called for stronger gun control regulation and improved access to mental health services. Although a relatively small number of mentally ill people are violent, receiving no treatment raises their tendencies toward violence, National Institute of Mental Health director Thomas Insel said.