Human age doesn't matter. He is developmentally a "newborn" in dragon age. Imagine u adopt a puppy. At 8-9 months, it starts humping your leg. Now, that dog is adult in dog terms, but it still doesn't make it okay. Same thing here, Hyoun make look like an adult human, but he/it is a "newborn" dragon according to other spirits, and Taehyuk has raised it since it was a youngling. It doesn't matter how Hyoun sees him, Taehyuk never saw him as a lover-material. More like a son or a pet he was responsible for.
it doesn't really matter how hyo-un saw him. What matters is the fact that taehyuk saw him as a child he was raising and taking care of. Taehyuk himself has never harbored any other feeling other than a variant of familial love and care for hyo-un. So even if hyo-un himself isn't looking at taehyuk that way, it's undeniable that taehyuk raised him in a sense. It's also true that their maturity levels (despite supernatural age or whatever) are inherently very different. That's all my argument is. Though to be fair, at the end of the day, this is story is purely fiction. I'm just looking at it through another way since I have mixed feelings lol
yk i was okay with the whole plot progression up until now cause we already established hyo-un isn't necessarily a human therefore his growth and development process surely can't be the same either. HOWEVER,,, with this new chap it really has gotten hard to defend this whole thing cause it's actually weird.. you really can't argue his age here cause he's clearly immature for his body stature.. so the whole thing is just.. really odd now