A high percentage of young girls between the ages of 9 and 15 are concerned about their weight and have gone on diets, with 50% of girls aged 13-15 believing they are overweight, 80% of 13 year olds having dieted, and 40% of 9 year olds having dieted. Obsessive Compulsive Disorder most often develops in patients between the ages of 13 and 18.