I had a complete hysterectomy about 9 years ago so menopause will be my choice. I currently take hormone replacement therapy. At the time of the hyst, I was already taking hormones to control peri-menopausal symptoms. The hormones apparently caused fibroids to start growing out of control. Since the doctor feared it might be cancer, we went straight to the hyst.
The short answer - early to mid-40's
Peri-menopause can last a long time. Peri-menopause is the time when you get the hot flashes and your period gets erratic. Not only are their hot flashes but you get "cold flashes" too which is when you can't get warm to save your life. No one ever tells you about those. And it can get a little hard to think. Not only is your period unpredictable as in it doesn't happen for a long time and then it comes or it get really light but you can also suddenly get gushing and your period feels like it'll never end.
Menopause is defined by the time when your period has stopped completely for 2 years.