The two planets most consistently lively in a psychoactive fashion during the midlife transition are Saturn and Uranus. Prior to the sighting of Uranus in 1781, Saturn was the ruler of the sign Aquarius, and as with all the signs with modern rulers, the ancient ruler is not only still effective, it acts as a highly significant agent in the sign’s behavior or manifestation.
http://www.astro.com/astrology/in_midlife_e.htm