What are some basic characteristics of menstruation?

Women begin menstruation around age 11-14, and continue until menopause at about 51 years old. The monthly cycle lasts about 28 days, but may vary in length among women.

Most girls begin menstruation between the ages of 11 and 14, although younger or older cases have been recorded. The first menstrual cycle, called the menarche, represents the beginning of the reproductive years, and continues until the beginning of menopause, around the age of 51 for most women.

Varying widely from woman to woman, the typical menstrual cycle usually lasts about 28 days. This cycle may be strangely predictable for some women and highly irregular for others. In some cases this variation may be attributed to stress, diet, or rigorous exercise.