I was thinking Doom as a sort of watershed moment in gaming, and going earlier than that and you could argue those titles belong on the already-existing retro gaming communities.1993 actually had both Doom and the first FIFA, it's got a lot going for it as a start year.
Looking at releases for 2013 though we have things like GTA V, BioShock: Infinite and The Last of Us. I definitely would hesitate to call those "old school games". 2011 has Skyrim. Does that qualify? Otherwise I'm starting to feel more drawn to the 1990-2010 timeframe; nice round numbers and should sort of capture the era of classic gaming. 2010 has Red Dead Redemption 1, Mass Effect 2 and Civilization 5. Is it fair to say those are some of the last old school games or do we need to go older? A two decade window seems good.
I agree that an open ended timeframe would lead to lost focus over time. If it's 10+ years old as the criteria, it would mean we're just 2 years away from The Witcher 3 qualifying for a community meant for stuff like Fallout 1&2. That just feels... wrong.