Premodern women rarely had periods, definitely not one per month. Breastfeeding suppresses menstruation, and children used to breastfeed until they were 4-5 years old. Famine and malnutrition also suppress periods. A few centuries ago the average French woman had her first period at age 18. Women who over-exercise (gymnasts) or who go on fad diets (such as raw veganism) don't have periods. My wife (because of breastfeeding and pregnancy) went about five years without a period.