CALLED Puberty. Puberty is the time in life when a boy or girl BECOMES sexually mature.Girls develop breasts and start their periods.Boys develop a deeper voice and facial hair will start to appear.The average age for girls to BEGIN puberty is 11, while for boys the average age is 12.TermDescriptionMenarcheIt is the occurrence of a first menstrual period in the female adolescent.Menstruation is the monthly shedding of the functional layer of the uterine ENDOMETRIAL lining that occurs when ovulation is not followed by fertilization.It occurs approximately every 28 days, with a RANGE from every 21 to every 45 days.MenopauseIt is the time in a woman's life when her period stops.It usually occurs naturally, most often after age 45.Menopause happens because the woman's ovaries stop producing the hormones estrogen and progesterone.