The length of the menstrual cycle varies from woman to woman, but the average is to have periods every 28 days. Regular cycles that are longer or shorter than this, from 28 to 35 days, are normal.The menstrual cycle is the time from the first day of a woman’s period to the day before her next period.Girls can start their periods anywhere from age 8 upwards, but the average is around 12 years. The average age for the menopause (when periods stop) in this country is 51.Most of the time, irregular