Even the people who've had experience with addiction, molestation, abusive fathers, hysterical mothers, horrible politicians, and Russian sporting events are not necessarily experts. At least not in the classic sense. They can be experts about themselves, their experiences. But no one else, no one else's experiences.
Aging is something young people will always -- understandably -- view with a mixture of dismissal and dismay. The response to the idea of senior sex is a bit like the response to the horrific acts of a survival series: we don't want to go there, but there is pleasure to be found in imagining from a safe distance just how difficult it must be.