
I'm guessing Chanwoo must be around 5 or so years younger, so not really a big gap. Chanwoo is probably just into 18 year olds so he's the one who is a bit of a creep if anything (⌒▽⌒)
Guessing Dong-gyun and him around mid twenties, given they have done their military service, although I might be completely wrong so apologies in advance .

He's expecting Jiwon to be "BJ Alex" in his private life, and is not respecting that this makes him annoyed. He's asking for things like a "private show" and that he wears his mask. Even when they were out on their "date", Dong-gyun commented that he was "happy to be spending time with Alex", he never said he was happy to be out with Jiwon. I think maybe the conversation Jiwon had with him, about feeling insecure about his weight and having to diet maybe prompted Dong-gyun to realise that Jiwon is a real, flawed person just like him, rather than this perfect "Alex" character.

SPOILERS

where r fantranslatiosn?

Thinking about him as ex or asking for a private show is not reflective of whether or not DG sees him as human or not. Obviously, if I met RM I would think of him as RM and not Namjoon, cuz thats what im used to. That, however, does NOT mean that I think of.him as less than human, as you're saying DG is doing. He realized that someone he admired was close to him, so yeah, he's going to have expectations.
Also, how is asking for a private show bad? Hes a fan. He will ask for favors like that, because thats just what they are: favors.
HE'S 32!? Made it a little creepier even though he's really handsome.