Menopause is defined as the absence of menstrual periods for 1 year. The average age of menopause is 51 years, but the normal range is 45 years to 55 years. The years leading up to this point are called perimenopause.This term means around menopause.. This phase can last for up to 10 years.enopause is defined as the absence of menstrual periods for 1 year. The average age of menopause is 51 years, but the normal range is 45 years to 55 years. The years leading up to this point are called perimenopause. This term means around menopause..