Hormones are the body's chemical messengers that guide the body's growth, sexual maturation, and many other body changes and functions. Exactly when these changes begin to happen depends on your own body's schedule. Puberty in girls usually starts anywhere from age 8 to 13, whereas in guys it normally occurs anywhere from age 10 to 15. During puberty, both guys and girls gain weight and start growing hair under their arms and in the pubic area. Girls' bodies get curvier as they start to develop breasts and later experience their first menstrual periods .
Guys get more muscular and their voices become deeper.
Guys also notice changes in their sex organs, like the enlargement of their testicles and the widening and lengthening of their penises . While all these changes are happening, usually there will be a growth spurt - a period of really fast growth. During the peak of a growth spurt, it may seem like you're sprouting up overnight. Although rapid growth spurts are normal, growing more gradually is perfectly normal, too. Once you start growing faster, though, you'll probably continue to grow taller for about the next 2 to 5 years.