How many years does it take to go from normal to the end of menopause?

The perimenopause. The average age of menopause is 52. Menopause is defined as one year without periods. The perimenopause is the period of time from when your periods become less predictable until the actual onset of menopause. The perimenopause does not begin before the age of 35 and usually does not begin until after 45. Perimenopause is because of fewer eggs, menopause is from the lack of estrogen.