There is definitely an age gap but they are all adults. I’m assuming since he was Yuri’s teacher when Yuri was in High School he must be like 5-6 years at least older. But Yuri is in college now and not his student any more and I think that age gap between adults is fine. Not that big.
does this story have an age gap? i don’t really like age gaps in any manga/webtoons so i won’t read if there is one.