Denny's right...your taste buds are your best guide. As he and others have pointed out frequently on the boards, any beer is ready when you decide it is ready. I do prefer a good amount of age on most stronger beers, reflecting brewing tradition, but that's just personal choice based on what I like and the frequency with which I brew (rare is the time when I don't have a couple Cornies with at least 6 or 8 month old strong ale in them).
As far as letting 'green flavors' age out, that's certainly an important step to me when I'm making IPA. I like a long aged IPA (even if only because my favorite commercial example was one that was bottled at one year). But that's just personal choice, as well as merely stubbornly clinging to my own preconceived notion of what the style is to me (besides...most of what we have always heard and read about IPA and it's history is evidently wrong anyway).
The fact is a lot of people like the 'green' flavors in a young, hoppy beer like IPA and for them, some of these flavors even define the style (and many folks don't even characterize them as green flavors at all).
It's all pretty subjective.