Good article. One objection: Implicit in “sex becomes more tiresome” is an assumption that sex was tiresome for everyone you interviewed before they reached 90. That’s a big leap for you, the interviewer, to make. Is that your personal feeling about sex? If so, I doubt it represents everyone with whom you spoke.
I know people in their 90s and upper 80s who miss the sensuality of sex and still have sexual thoughts and desires, even if their physiology no longer supports certain sexual acts. I also know people in this age group who have lost desire. And I know people in their 50s, male and female, who have lost desire. The topic of sex for the very elderly is worth an article itself and cannot be summed up in one sentence containing the phrase, “sex becomes more tiresome.”