Well, I can tell you that "normal" heterosexual sex life goes downhill pretty fast as you age. As a man, your wife is likely to dislike sex after menopause, and even if she doesn't, it can make sex much less pleasurable and even painful because all the soft places waste away. I suppose that it is nature cutting you off because your sex life is no longer important to procreation.
As a zoo, my sex life is still exciting in my late 70s. I may not be able to cum every day, but I at least poke one or two girls. I am still a horny teen at heart and mare pussy is always there! After a dry spell, I can cum in mares twice a day for several days.