Here is a link to the NZVCC website page for vehicle classes:

Click here

Note that all vehicle types are catered for by NZVCC including cars, motorcycles, commercial vehicles and Factory Built and Historic Racing Vehicles.

In summary the classes are mainly by year-to-year periods:
Veteran: Up to 1918 inclusive.
Vintage:      1919-1931 inclusive.
Post Vintage: 1932-1945 inclusive.
Post War:     1946-1960 inclusive.
Post 60:      1961-1980 inclusive.
Post 80:      1981 onwards but over 30 calendar years old.