Having reead through all the definitions there only seems to be one correct, and apparently, only one written by someone over 20. If you're not in you thirties it was likely you missed it. A greebo listened mainly to the Poppies, Neds etc, not metal or rock(especially not Iron Maiden). If you weren't around in the early 1990's them I'm afraid you're just a wannabe. Sorry kids! But definately keep on trying to keep the contemporary alternative scene alive.
Visit a Wonderstuff concert and they all appear from mid-thirty-greebo-land.