From my perspective, if I were a woman — in this case, Sue — why the hell would I let some old man fuck me?
Maybe i'm drifting off completely now. But - what most people tend to forget:
Men and women have completely different reasons for having sex, and the selection of their sexual partners. These reasons are dating back to the hundred thousands of years before modern civilization, and are a firm part of our DNA hardware.
We men always look for younger, healthier, prettier partners to spread our genes to as much offspring as possible. A man could impregnate at least one different woman per day, that's why we always want sex and would have it with every halfway acceptable woman if we could. And then we could just walk away and let the women and their "clans" deal with the offspring. It's there no matter if we support it. This would be a valid gene distribution strategy, just as loner animals like bears are doing it.
Women however can only get pregnant with one child at a time, and each child is a long-term engagement with huge risks. They have to carry the offspring for 9 months, give and survive birth, feed and raise it for the next 10-20 years. That's why women are always looking for men with a better social status, more power, wealth, or at least the ability to protect them from any outside harm.
Additionally, women have a hard limit on their fertility after which their body changes completely into more of an intergender form. They lose not only the ability to conceive children, but also lose all their attributes of female attraction within the turn of a few years. While men observe a much more linear aging process, keeping the ability to conceive children well into the final stage of their lives, and usually just hoarding more power, wealth and influence along the way.
So while most men would never consider sex with women older than them, or merely not fulfilling their beauty standards, women have absolutely no problem whatsoever taking a much older, uglier man as partner. As long as he can put food on the table and all that.
Only reason why we settle for monogamous partnerships with partners roughly our own age, are the societal structures required to maintain stability. Otherwise men would just be busy fighting over the right to mate, like most animals do.
So back to the question: Indeed, Sue would have no interest AT ALL for having sex with her old father-in-law. But not because he's old, but because he has nothing to offer in the biological-anthropological sense.