Visible signs of adolescence include growth spurts and the appearance of pubic and axillary hair in both genders. Girls develop breasts and boys grow facial hair. Signs of early adolescence typically emerge between ages 11 and 14 and include physical, emotional, sensory and motor development, according to WebMD.
Parents may notice that adolescents withdraw somewhat from family activities, preferring the company of friends, states WebMD. Some adolescents grow more awkward as their brains acclimate to rapidly growing bodies.
The endocrine glands produce hormones responsible for the development of estrogen and the onset of menstruation in girls. Hormones produced by the endocrine glands signal the testicles to increase testosterone production in boys, states The New York Times. Increasing armpit perspiration, body odor and acne are also signs of adolescence.