As females age, their bodies typically undergo two significant changes that generally occur during adolescence and middle age. The first, known as menarche, is the time during puberty when a girl begins having monthly menstruation cycles, which often tends to range from 8-13 years of age. She enters the second change, known as menopause, 12 months following her last menstruation cycle when her ovarian function ceases, usually sometime in her 40s or 50s.