I think Yoon will age, but slower because he is a half-blood vampire. I read the QnA section so it's from reliable sources lol (=・ω・=)
Yoon is only half-vampire, hence his body being unstable and needing to absorb human energy instead of drinking blood at some point in his life. It has been explained in the webtoon that he leans more to his human side, his vampire side only slows down his aging process which is why he looks young even if in reality he's 31 y/o. His lifespan isn't affected much so rest assured that he'll grow old on a similar rate with Kangwoo (seme).
I'm just wondering like Yoon is a vampire right? so he won't age?? like if he will not age then the seme will have to grow old by himself and yoon will watch him fade away by time????