Puberty
Illness. Boys and girls who are sick for a long time, especially with illnesses that cause them to have a poor diet, tend to start puberty late. For example, this often happens to people who suffer from anorexia nervosa. Anorexia nervosa, often called "anorexia" for short, is an eating disorder. People with anorexia think that they are fat, or are very afraid of becoming fat. They try to lose weight by eating too little and doing too much exercise. To avoid gaining weight, they do not eat the amount of food their body needs. This causes them to stay at a weight that is not normal for their age and height.