Menarche
Menarche is the first menstrual cycle for female human beings. From medical and social perspectives it is often the central event of female puberty, as it signals the possibility of fertility. Girls experience menarche at different ages. The timing for menarche is influenced via female biology, in addition to genetic and environmental issues, particularly nutritional factors. The average age of menarche for the United States is near 12.5 years and 12.75 years for Canada.