In Heaven by JYJ and Severely by FT Island, these two feel so much like dramas, one other feels like it should be a sci-fi movie Error by VIXX, try them all and you will see. ^^
I loved this drama, as for the age difference causing less romance, haven't you heard of pure love, loving the person with not as much skinship. I never found it boring and I have lost count on how many times I have rewatched it from beginning to end, it never gets old, hell if they had a book that was exactly like this I would read it in a heartbeat. ^-^
I just noticed something on the poster, the guy in the far left isn't he the army guy from the Iron Dimension in KO One Return. I hope it is him because I have wanted to see him again in KO universe, loved his crazy character (Spaceman). I hope its true, when it starts I guess I'll see. ^-^