We live in a world where so much, if not everything is transient. Passion too can flit away over the span of time, and there are those lovers who feel the empty pang of sexual zest long deceased. Thus the fact that they are not having the wild and carefree sex of their twenties and thirties may result in a period of adjustment, confusion, and a certain resistance to abandoning the ways of their youth. This is also a major phase in a person's life. Children are growing up, perhaps leaving home.
Work is all consuming and life is racing ahead with the incessant ticking of the clock.
Women may be confronting menopause and men may be confronting their own psychological and physiological changes. For many, this may not be the sexiest decade for a couple to face. This may also be a time for some when marital dissatisfaction bubbles to the surface. Starting in the 30's, a significant percentage of people say that the frequency AND quality decrease over time. On the other hand, most people, of all generations, feel that the quality is enhanced as the frequency admittedly diminishes.