By IL DMV 20 years is antique. Yet I don’t consider myself a antique and Most don't consider stuff made in there lifetime antique US Customs office considers a 100 Years as antique and vehicles at 75 Years But Each state if different on vehicles So if You go Buy the US Customs office Then No Garden tractor as we know them today is a antique But I would say a 30 Plus Year old Machine is at least a Classic or Vintage if antique would not fit:thThumbsUSo, a '90 car is an antique now? I don't think so. I'm almost 65 and I think anything made when I was a kid is an antique. Anyway, these catagories probably won't mean anything until some kind of national governing board makes them official.
It's true that old cars don't have the metalurgy/technology of the new ones. Still they were overbuilt. They had heavier gauge metal in the body and extra iron in the block and such. The same with GTs. When did the builders start saving money by making them flimsier? Using alternative materials such as alloys and plastics.
Let me ask another question: what is the Golden Age of GT styling? I would say the late 60s. For cars it was the mid to late 30s.
Plastic has been around since 1856, Fiberglass since WWII Deere used fiberglass Hood's from the early 1960 until the early 90's:thThumbsUMissouri uses the term "Historic Vehicle" and will issue a permanent tag to a vehicle 25 years old.
On vintage garden tractors I'm with the line of thinking that plastic hoods and cup holders weren't standard equipment.