What's the earliest someone can begin menopause?

Menopause: Nonsurgical spontaneous ovarian failure (menopause) affects about 1% of women by around age 40, and only 0.1% of women by around age 30.

20s: Premature ovarian failure (Menopause at a young age) isn't common. At age 35 the incidence is 1 in 250 women. At age 40 it is 1 in 100 women. It does occur in the 20s but is very rare. There is frequently a genetic abnormality present when it occurs in women under age 35. Best wishes!