The reasons why boys are not taller include genetic factors, nutritional factors, lack of exercise and diseases. 1. Genetic factors: height is greatly influenced by heredity, if a boy’s parents are not tall, then the boy’s height may not be very high. 2. Nutritional factors: growth and development requires adequate intake of a variety of vitamins, proteins, calcium and other nutrients, if in the process of development of the male lack of nutrients, it may cause the situation of not tall. 3. Lack of exercise: Exercise can promote the absorption of calcium, which helps muscle and bone growth, and lack of exercise during the developmental period can also cause a lack of height. 4. Disease factors: hypothyroidism, growth hormone deficiency, chromosomal disorders, developmental delay and other diseases may also cause height abnormalities, which can be diagnosed by perfecting the relevant examination. Boys who can’t grow taller are advised to go to the hospital to get a clear picture of the cause.