The Style section of the NY Times has a Sunday column on "Modern Love" written by a different person each week, and sometimes it deals with sex issues.  Last week's column (link below, 8 March) came from a 57 year old guy whose wife became totally disinterested in sex, much as they still loved each other.  After becoming increasingly frustrated, the guy was further dismayed when his wife developed early stage Parkinson's.  However, as part of her treatment she began taking meds that made her compulsively obsessed with having sex, to the extent that they were going at it 9-12 times per week and he was getting worn out.  He began avoiding sexual encounters with his wife, but her demands continued.  Well, Parkinson's is no laughing matter but this is pretty amusing.  To see what happened, check out the link.  Incidentally, I seriously doubt whether even a healthy 57 year old guy can have sex to completion 9-12 times a week and keep it up (pun intended) for long.  Many women can do so, for a time, I believe, but they as well as men are dependent on how much testosterone they produce and they run low on the supply in menopause, so I have read, but men continue to produce testosterone, but in smaller amounts, even if they have ED.  This accounts for the phenomenon of "randy old men," and "cold wives."  
Anyway, FWIW:     http://www.nytimes.com/2015/03/08/style/finding-equilibrium-in-seesawing-libidos.html?rref=collection%2Fcolumn%2Fmodern-love&_r=0.