According to Mayo Clinic, the average age in the United States at which menopause begins is 51. However, menopause can happen in someone in her 40s or after age 51. Menopause occurs after a woman's last menstrual period, signaling the end of menstrual cycles.
According to Mayo Clinic, only about 1 percent of women experience menopause before the age of 40. The months or years prior to menopause are referred to as perimenopause. Women may experience symptoms during this time including hot flashes, night sweats, difficulty sleeping, mood changes, weight gain and irregular periods. Menstrual periods typically occur between two and four months during the time of perimenopause.