When I started collecting in the early 70's, anything un-styled or 50 years old was considered antique. Styled tractors, or roughly 30 years old were classics. Then up until the early 60's were considered vintage. Here tractors like your 4020 weren't even considered, they were still working in the fields.
But here we are 50 years later, and I still have a tendency to classify them the same way. Yet, someone 25 years old would consider it an antique.
It will be interesting to see the reply's you get. It's going to be like the ages old question, "What's the best oil to use..." LOL....