The average height for a 14-year-old boy is 64.5 inches, while for a girl the same age, it is 62.5 inches. The height disparity increases as the children become young adults; 20-year-old males average 69.7 inches in height while 20-year-old females are 64.2 inches tall.
This trend generally begins at age 14; adolescents of both sexes are within 0.2 inches of each other for average height at 13 years of age. After age 15, males on average are 4 to 5 inches taller than females. The sudden height increase of adolescence generally stops by age 17 or 18, seen culturally as the onset of adulthood. From ages 17 to 20, both sexes gain less than an inch of height.