Why do we assume that as we age, our desire for sex is going to fade?

Why do we assume that as we age, our desire for sex is going to fade?

Dr. Ruth, Westheimer, PhD, Sex Therapist:

God forbid! Don't assume it. People after 50 should continue to have a wonderful sex life if they so desire, if they say they don't want it anymore, I say goodbye, but if they so desire, but they have to be sexually literate. A woman has to know that after menopause she needs a lubricant, not to engage in intercourse with a not well lubricated vagina, it's painful, she's going to say, who needs it. And men must know and even physicians don't know, that after a certain age, there is no psychogenic erection. After a certain age, a man does not have an erection when he wants one, when he thinks about sex. A man needs physical stimulation, rubbing against the partner, his hand, or her hand on his genitalia in order to obtain and to maintain the erection.Here is what happens. They are trying to have sex, he doesn't have an erection, she thinks I'm not attractive any more. I don't look, my body has changed, I don't look like I looked 10 or 20 years ago, and then there is more to that. She also doesn't want to have the feeling that she is going to make him unhappy, because if they try to have sex, and he doesn't have an erection, he gets very unhappy, so she avoids it. There is an avoidance pattern by both. Then he starts to think, I would like to have sex but I know I have problems, and if he thinks that, he can be assured that he is not going to have an erection. Male sexual apparatus is very delicate. The moment he thinks, oh my gosh, what happened to me yesterday is going to happen again, he will not have an erection.