나이차이 정말 많이 나지 않아?(informal) There's a big age difference between the two. 나이차이 쩔지 않아? (very informal) There's a f*cking big age difference between the two. I hope this will help you. If you are helped, please click the best answer.

that means actually presents that the gap of age is very big. however, 쩔지 않아 is a slang that's been used recently in teens, so, I don't recommend you to say that :P

나이차이 = age difference 쩔지 않아 = it is like you can't help something about it 나이차이 쩔지 않아 = you can't do anything about the age difference