At what age does perimenopause start?

Everyone different: Average age 45+/-, signaled by irregular periods. Early perimenopause cycles different by 7 days or more, late perimenopause(pm) starts with no period more than 60 days. Starts and stops. Most symptoms(sx) in late pm, but symptoms like night sweats and hot flashes and sleep disturbance in days before eriod can start when periods still regular.