The age of adolescence falls between the ages of 13 and 19, when boys and girls gradually change from children into young adults. During these years, many physical, emotional, mental and social changes take place. Although adolescence is caused by changes in hormones, the exact age that boys and girls go through it depends on different factors. Parents who experienced adolescence at an early age are more like to have children who start adolescence before their classmates. Children who are nutritionally deficient are more likely to have delayed adolescence. Generally, girls mature faster than boys, often starting adolescence earlier and finishing earlier.
In addition to increasing height, endocrine glands excrete hormones that help in the development of secondary sex characteristics. Hair begins to grow on the face, under the arms, and in the pubic area in boys; their shoulders become broader and their voice changes. Physical changes in girls include their hips becoming wider, breast development, the monthly cycle of menstruation, and hair growth in the armpits, the legs and the public area. As mentioned, due to girls' earlier maturation, they usually reach their full height by the age of 17, while boys are very likely to still grow at this age.
The Canadian Pediatric Society, on the other hand, resists restricting adolescence to a specific age bracket. Their position is that adolescence starts when normal puberty begins (to exclude artificial puberty brought on by medications, etc.) and ends when the teenager is expected to act like an adult. The age range corresponding to this definition is around 10 to 19 years old. Occasionally, adolescents may need care in a facility that has age limits (for example, a children's hospital), but the Canadian Pediatric Society believes that people who are responsible for the health care of adolescents should be flexible regarding the age guidelines.