Our rule of thumb is 25 years or older for that body style
I can't find the thread, but in the previous discussions about defining what is classic, antique, nostalgic, etc., remained debatable.
There were lots of comments that anything without chrome bumpers and carburetors could not be nostalgic.
There were some who placed importance on the vehicle being a milestone of design, engineering, racing, etc.
Someone suggested a ten year date because that is the date the US government stops requiring the vehicle manufacturer to provide replacement parts.
There were some that suggested that anything that has moved beyond the current flavor-of-the-month and what the mass market magazines and parts manufacturers/retailers are catering to. And whatever these would call "old school".
The comment from the moderators (quite possibly Ben) was that the use of the word "nostalgic" had no year or styling requirement and was intentionally vague in order to include more than it excludes.
It might be time to set up some subsets of the overall group, because at this point, the website serves everything from Toyota AA to sixth generation Civic, which isn't a bad thing.
I own vehicles with a wide range of ages. None are new, and some are counterparts to the 1994 Lancer. None were ever the flavor of the month, or new school, so none could ever be old school. And much of my work on even the newest of these vehicles has turned toward restoration, which may be the best indication of how these vehicles should be classified. I consider all of them "nostalgic", and consider myself in good company with something like an Evo II.