First off, I'd like to say to all you young whippersnappers out there, stop saying eww. We older people have as much right to a good sex life as you do. Just remember only the lucky get old and if you're lucky enough to get to my age, you'll want to get laid too. Next, the only qualifications I have to talk on this subject are of a personal knowledge, as I have no professional training in this field.
Everyone, man or woman has a right to an active sex life no matter how old he or she may be. However, having that right does not necessarily mean you or your partner has the ability to fulfill that right. In most people, aging is a gradual process and we tend not to notice our loss of stamina and a lowering of libido. Many couples are amazed when they find out how long it has been since they've been intimate. There appears to be a certain time line and once crossed, sex disappears between them. It is an unconscious decision that we make, that going without is just easier than having sex.
Our sex life began declining after my wife went through menopause. As the closet sub in our relationship, I always enjoyed letting my wife take the lead in not only our marriage but particularly in the bedroom. With the hormone loss, came a lessoning of desire from her and although still willing to participate, she no longer had a strong sex drive. When you add in less lubrication and my no longer rock hard erection it tended to make sex work instead of pleasure.
As I kept getting the feeling that she was merely allowing, instead of wanting sex I would often fail to achieve orgasm and just give up. My wife took this as a lack of desire for her, further complicating our sex life. She interpreted my failed performances as a sign that she no longer had a desirable body. I repeatedly told her this wasn't true but to her she had my feeble erection as all the proof she needed. She told me many times that she didn't miss the sex as much as she missed the post coital cuddling. As for me, I just couldn't bring myself to tell her it wasn't her body that failed to turn me on it was her lack of a sex drive.
Everything physically appeared to work for both of us just not well enough for us to have sex. I turned to internet porn and masturbation and although not hard enough for intercourse, I would be firm enough to achieve orgasm. My wife turned to romance novels for much of the same reason. I kept jacking off and she kept losing herself between the pages of Harlequin as the clock kept ticking. It didn't take long before we just quit trying, weeks turned into months and months into years.