Adolescence: This is defined as the transitional period from childhood to adulthood usually encompassing the ages of 13–19.
How do we know when we are in our adolescence years (besides our calendar)? Well, it is marked by puberty. During puberty, boys and girls have many physical changes such as growth in height and weight, pubic hair, facial hair in boys, deeper voices for boys, breasts and menarche for girls. Due to the hormonal changes in boys and girls, this time period from ages 11–19 can also be very emotional.
Puberty Time of sexual maturation—when girls and boys begin physical changes in their bodies.
Menarche The onset of a girl's first menstruation (period.)