While some of them are content to be alone, they often prefer to spend time with friends. Difficulty sleeping, refusal to attend school, changes in appetite, or loss of interest in activities can be signs of a mental health issue. Common mental health problems. Normal Development: Middle Adolescence. Most year-olds can communicate in an adult-like fashion and are able to hold appropriate conversations. Longitudinal models of developmental dynamics between reading and cognition from childhood to adolescenc e. The Growing Child: Adolescent 13 to 18 Years. While some teens may be imagining college, others may be thinking about getting their own apartment. Unless you see warning signs of mental health problems, an increased desire for privacy can be normal.