The ‘what’ has been explained pretty well in other comments, the strange thing is that Milo didn’t immediately go on offense in response.
For all the normalizing of homosexuality that has occurred over the past two decades in popular culture, the concept of gay teenaged boys interacting romantically witj older guy men is stubbornly resistant to the culture wars.
Young straight guy with older female? Hot for Teacher or Mrs. Robinson. Boy is given free rein to fantasize, older woman is expected by society not to act because younger male has nothing to offer her, but if the younger male is in the age of majority, the older woman is a ‘cougar’.
Young straight girl with older male? If the girl has a crush, at worst she is considered confused. Older male is at least expected to understand by society not to reciprocate or pursue until a certain age, but men are generally given free rein to fantasize so long as she hits the age of majority first. Successful men are almost expected to have a youthful ‘trophy wife’.
Younger gay male with older gay male? Totally verboten. not even in popular culture is it seen as acceptable to portray older gay men with drastically younger partners. Strangely, this was more accepted in years prior, but the concept of the ‘old queen’ is apparently antiquated and unacceptable.
Remember, It doesn’t matter what is actually right or wrong with the Milo haters, it only matters to them that he is destroyed. If some of their hypocrisy is a casualty of these skirmishes, all the better.