Does it start in the mid twenties, late twenties or in the thirties? Although the average age for menopause has been said to be in the thirties to somewhere in the fifties, there has been no specific age boundary which determines when a woman stops being fertile. Yes, science has said that the chances decease significantly as a woman advances in age but there has been stories of women in their late forties and fifties who are still have their menstrual cycle. In writing this I researched on the latest a woman could still have her menstrual cycle and was shocked to read woman in their sixties still underwent the process, though they were few and far in between.
On the other hand there are stories of women in their early twenties who have undergone menopause. For instance I remember an article I read of a twenty year old girl, who had already gone through menopause. She was said to have undergone premature menopause caused by premature ovarian failure (POF).
This shows there is no hard and fast rule to when a woman undergoes menopause, it just simply depends on the individual woman and her body system.