A living entity is never satisfied with a woman unless he is trained in the system of brahmacarya. Generally a man's tendency is to enjoy many women, and even at the very end of life the sex impulse is so strong that even though one is very old he still wants to enjoy the company of young girls. Thus because of the strong sex impulse the living entity becomes more and more involved in this material world.

From Srila Prabhupada's purport to SB 4.25.44