Really the only problem I have with adult Iceman being so quick with it is how quick kid Iceman is. It's a little understandable that adult Iceman would be more repressed with years of practice and the current era makes understanding his sexuality easier for younger Iceman, but kid Iceman doesn't seem to have much "resistance" to the truth like adult Iceman would have. Talk about a guy where humorous denial and deflection comes naturally to him. Adult Iceman barely came to terms with his sexuality where kid Iceman was near immediate cool with it. I think as an unsure kid, the younger Iceman should've spent at least a little time trying to doubt what Jean said. Even if he knew it deep down he might not have "known" the truth since he had been actively denying it. It would've been better if it were introduced as doubt as opposed to kid Iceman just straight up lying. At least that's my take on it.