Last period ever occurring between the ages of 55 to 60 is known as a "late menopause". An "early menopause" on the other hand is defined as last period ever between the age of 40 to 45.
Rarely the ovaries stop working at a very early age, anywhere from the age of puberty to age 40, and this is known as premature ovarian failure (POF), also commonly referred to as "premature menopause". 1% of women experience POF, and it is not considered to be due to the normal effects of aging. Some known causes of premature menopause include autoimmune disorders, thyroid disease, diabetes mellitus, chemotherapy, and radiotherapy. However, in the majority of spontaneous cases of premature menopause, the cause is unknown.
Premature menopause is diagnosed or confirmed by measuring the levels of follicle stimulating hormone (FSH) and luteinizing hormone (LH); the levels of these hormones will be abnormally high if menopause has occurred. Rates of premature menopause have been found to be significantly higher in fraternal and identical twins; approximately 5% of twins reach menopause before the age of 40. The reasons for this are not completely understood. Transplants of ovarian tissue between identical twins have been successful in restoring fertility.

