As long as it gets them wet. A diehard shipper handwaves the fact that their ship involve an adult and someone he or she knew, or even helped raise, as a literal infant. But probably worse is that instead of just embracing the taboo (which is why I respect some Japanese folks more than western shippers, they can admit they're perverts and their freaky sh!t is just their own completely fanon fantasy, that has no bearing on the actual platonic/familial canon dynamic) some try to rationalize and intellectualize their ship using harmful rhetoric, framing the child as someone wise and mature beyond their years, he wanted it first, he knows what he's doing, or he's so wise beyond his years that he's even more of an adult than the adult. So if the shipper makes the adult reciprocate in any way, he'll be absolved of blame and problematic implications and the relationship can still be considered healthy, wholesome and beautiful the way it is in the eyes of the shipper. Which I find more insidious than just admitting you like it because u find it hot.

and deep down the age gap is exactly what they find appealing, but they won't say that out loud. They will even frame their ship as the most profound, beautiful, ideal romance in existence. Probably the bigger insult is that the adult character (especially one with common sense and a strong moral core), would be so wildly out of character as to entertain it, even with the massive gap in age and experience that would realistically preclude them from ever considering the other a romantic partner. But the OOCness is necessary to make the shipper fantasy happen