Yeah great question with varying responses. Vintage in general refers to an era, usually a decade in many situations. For example, this guitar is vintage of the 1940's era.
I thin the question being posed is what is the cut off year to be considered a "vintage" original SG. Off the top of me head, I would have to go mid-late 70's. I think a 76-79 SG is still vintage to me. This is of course in the context strictly of SG.
But in the broader picture I like to think of time frame in reverse of the present. For example, in 1990 they surely considered a 1969 Gibson SG "vintage". But in terms of time, that is only 21 years old. Heck, I have SG's I bought new that are that old, and they dont even relate to 1990's!
I think with guitars folks mix up Vintage with "Golden era". That's just another loose term, I get it. But many folks refer to the 60's, the inception decade for the SG, as iconic and vintage. That's all fine, From 1969 to 1970, that's 12 months... In vintage terms, a 1970 would become vintage the year after a 1969.
Most people could care less for a 1980 or 1990 SG; generally speaking don't get hostile. 1980 was over 40 years ago! That's a vintage guitar in my books. Think of any guitars that predate the SG. The Les Paul for example. To my knowledge its inception date was 1952. Do you consider a 1962 a vintage Les Paul? If so, why not a 1971 SG?
What about a 1972 Les Paul... Does that make the cut for vintage status? if so, why not a 1982 SG?
Technically saying you have a 2001 vintage era guitar is correct.
Oh god, don't add another definition of the word "vintage" to this!!!
Yeah, that definition is just another way of saying "dated to", like "this wine is vintage 2013". Obviously, when it comes to gear, most people are using the definition that more closely aligns with "antique" or "classic".
I'll say, when I was shopping for my Gibson in 2010, I was looking at 1986 SG-62s because they were the most affordable approximation of a vintage SG that I could find (and I was drawn by the "vintage mojo"), and I felt they were basically vintage already back then. I also thought they were a steal and could increase in value as they came to be appreciated as the first ever SG reissues and now vintage themselves. Eventually, I heard about the incorrect body shape of them and understood why they aren't higher valued, but they do remain a great value for anyone who doesn't mind that and just wants a player's guitar.
It is funny how guitars mirror vintage cars; the "purist" cutoff is around 1970-1972. With cars, it's because insurance companies started increasing rates on muscle cars (and to a lesser degree, but overblown by many enthusiasts, new pollution controls). That also coincided with the switch from SAE gross to SAE net horsepower ratings, making the drop in power ratings look even more exaggerated than it really was. With guitars, it was a lot of cost cutting thanks to acquisitions by larger corporate behemoths in a misguided attempt to compete with cheaper Asian guitars instead of leaning into their position as higher end offerings.
That said, officially, 25 years makes a car antique. It's funny seeing some older guys lose it when they see a 1995 Civic with antique plates. They still cling to that 1972 cutoff for a lot of classic car shows. It's pretty silly to say a '77 Trans Am or a Delorean or GNX aren't classics at this point, really. Now "Radwood" has sprung up to celebrate '80s-'90s classics because of that attitude.
I think the main reason guitars will take even longer for people to come around is that most '80s-'90s guitars were basically reissues of '50s-60s guitars, whereas cars of the time were their own thing.