An explanation of the classes defined by age:
On various pages, you will see references to veteran, Vintage, etc. These terms vary somewhat in their meaning, depending on who uses them, so for consistency I use the VMCC definitions (or a subset, to be accurate - I don't generally distinguish between Early and Late Vintage).
Veteran (or Pioneer): pre-1915. There are sub-classes for veteran events, but they needn't concern us here. The VMCC only specify Veteran.
Early Vintage: 1915 to 1924.
Late Vintage: 1925 to 1930.
Post-vintage: 1931 to 1944.
Post-war: 1945 onwards, but more than 25 years old.
The odd one is the most commonly-used: Classic. This has no real definition; for some people it covers all of the above, for others it means late post-war (Sixties and Seventies), for insurance companies it can mean more than 15 years old. As far as bike magazines (who use it more than most) are concerned, it generally means "more than 25 years old but not really ancient".