Oh.. It's very hard to write about it. I have found 도령 in dictionary and Naver. They said 도령 is a man who is an adult but doesn't marry yet. So, If bachelor measns "A man who has never been married." I think 도령 can be translated bachelor. Because people in Korea(Goryeo) or Cho-sun call ed the student who you said 도령, you can think 도령 as the student. But as I know they called a man who is an adult but doesn't marry yet 도령 and there was the class between them. So, maybe I think just only someone in 양반( it's like noble) was called 도령 It is so difficult to me , cause it is about history ^^;;;;.....