All women will enter menopause one way or another. For most, they will enter menopause naturally when their ovaries stop producing follicles for fertilization and estrogen. Others may enter menopause medically because of a treatment that suppresses or removes ovarian function entirely. But, if you go through menopause naturally, you will likely go through perimenopause, a transitional stage between when you have regular menstrual cycles to none whatsoever.
Perimenopause typically occurs in your 40s and 50s, but it can happen even in your 30s. Unfortunately, most people do not know what perimenopause is, as it certainly was left out of most health classes in school.