I have a question: Why is it that at early 15 males are thin and long and at the end of 15 males are bigger and look like adults?
It is not a factor of age but that stage of development a boy is in. Typically at the beginning of age 15, a boy is just finishing off his growth spurt. That rapid growth used up a lot of his body fat and his long bones make him look stretched or thin. By the middle of stage 4 (a year later), he is starting to develop muscles, which fill out his frame and gives him a more adult look.