I like older men too. ;) Good dramas with older males in the order of my preference:
Beethoven Virus (k) The age gap is not huge I guess (10-15 years?) combined with his experience, attitude and position as a leader, it fits my definition of "good age gap drama"!
The King of Dramas (k) Well, the same as above, just not quite as extremely wonderful. ;)
Iki mo dekinai natsu (j) The age gap is about 20 years. The romance is rather between the lines though, don't expect anything steamy, but I absolutely adored this drama!
Kou Kou kyoushi 2003 (j) 30-something teacher and high school student. It's a very... special drama; the plot is something I've never seen before or after. Strange things are going on but as I was watching this I really wanted them to live happily ever after!
My rainy days (j) It's a movie, high school student meets older man.
Mitsu no Aji (j) Girl falls in love with her father's younger step brother (meaning the man is older but not old enough to be her dad). This is about the "incest" thing more than the age gap (about 10 years?) though. Melo but I loved it.
Go! Goal! Fighting! (c) This is not mainly a romance drama (it's a feelgood "we can do this if we work hard together and listen to our teacher!" drama) so that's why I put it at the end of the list even though I adored it. The guy is 30-something and the girl is 20-something so the age gap is not more than like 10 years but it's there and noticeable sometimes. The romance is more important in the later episodes.
Valid Love (k) High school girl falls in love with teacher. They meet again years later. The age gap is a bit of a thing here. I liked the drama; lots of people loved it but I though it was dragging towards the end.
The Painter of the Wind (k) Historical. A girl is disguised as a boy and she's trained to be a painter. He's a teacher. There's a mystery too, some people who died 15 years ago and he tries to find out the truth. There's also a bit of a lesbian subplot as there's a woman who mistakes the girl as a boy and falls in love with her. I thought this drama was very interesting (the importance of art in ancient Korea) and the leads had chemistry and all... but I found some parts a bit confusing and it is a very slow-paced drama. Age gap is about 20 years.
Also, the only "noona romance" I've actually liked is Secret Love Affair! (That's because in many dramas with an older woman, she is acting more like a teenager. I like the kind of dynamics like in Beethoven Virus but reversed roles!)
What about you, have you watched any good age gap dramas that haven't been mentioned here yet? I like this theme so I want more. :)