More-or-less the same criteria, though more like 2008-2011 by my own subjective standards; I was already active (well, lurking while working on my own UTAU projects) in the community by 2012 so that era felt "new" to me at the time. Also it's hard to think of my own VBs are being "classic".
To me it also has the implication of being at least somewhat well-known for it's era. I wouldn't really call obscure voicebanks that never really gained traction classics, though ones that don't seem to get talked about as much these days might still count if they were at the time.