The idea -- "I would hazard a guess that most such relationships pair much older men with much younger women--while again acknowledging that there are exceptions to this generality. Given the prevalence of sexism, such relationships seem to raise reasonable suspicions that they are embodiments of widespread sexist attitudes towards women, who suffer disproportionately from discrimination as they age, and for whom standards of attractiveness (including youthful appearance) are especially oppressive" -- ignores the mountain of evolutionary biological, sociobiological, and evolutionary psychological work done in this area that suggests that the pattern older man-younger woman is to be expected. This work might very well be false or full of oversimplifications, of course, in which case the charges of "oppression" and "sexism" in the pattern might be rightfully made. But the idea quoted too cavalierly writes off the evolutionary/biological underpinnings of such a pattern.
Why is it considered morally wrong for a man or a woman to have a romantic or sexual relationship with someone significantly younger than themselves?