Being keen is a good thing I think. If your keen, then you have a sharp eye on stuff.
Missing UK(?) slang sense?Edit
I think we're missing a sense, or a shade of usage, in British English, which relates to somebody being over-eager to attain academic success, or a "swot", or teacher's pet, etc., who works very hard. Compare keeno. I've heard it around the university now and again. Equinox ◑ 04:00, 7 May 2015 (UTC)