A childhood belief about periods

When my mother first told me about periods (I was maybe five or six) she said, "You first start your period around eleven or twelve. You go through menopause in your 40's." I took this to mean that once you started your period you had one, continuously, until you reached menopause. I was very suprised when my first period stopped (I even went so far as to ask her if anything was wrong with me). My mother says she was shocked to discover I not only had I developed this odd idea, but that I hadn't been upset about it at all! I just figured, since my mom told me it was natural, I'd just go with the flow (no pun intended).