The new generation seems to be really sensitive to age gaps and his relationship with Momo seems to have rubbed them wrong. He also has a blunt/teasing personality which I think some take issue with, especially around dynamics involving female and male relations.
He seems perfectly fine to me. And seems on good terms with and has a lot of friendships with many idols, both female and male. If they had a problem with him they don't seem to show it.
As for the age gap? I don't see the issue. Momo was an adult. I think people are infantalizing Momo. But I'm from a different generation. My parents have a 10 year age gap so I think it's fine. I get people's concern but I think they take it too extreme and deny adults agency.
i think the age gap with momo was kind of the tipping point for a lot of people i didn't think it was that weird but i'm 13 yrs apart from my partner so i'm biased lol