Adolescence
During adolescence, your body composition changes dramatically. The differences in body composition - both fat and lean body mass - between girls and boys are very small during infancy and childhood. However, they become significant during adolescence.
Although they usually mature more slowly, boys tend to add more lean mass and less body fat than girls during adolescence.
Girls put on more body fat than boys during adolescence. This is perfectly normal and healthy. A female should always have a higher percentage of body fat than a male of equal fitness because her amount of essential fat is higher and her reproductive function requires more energy. (For more information, visit BODY FAT BASICS)