Just did a quick search on the net for definitions and I really think what is below sums it up for most of us rather than having three hundred different classes.
I'm sure that most of us enjoy a wine or three so I have left the whole definition intact. definition #4 pretty well sums up our sport / hobby I reckon so no further bullshit required other than setting up age classes. All the bikes can be vintage be they motocross trials or enduro.
This is the web based Collins dictionary definition;
vintage (vintages plural )
1 n-count The vintage of a good quality wine is the year and place that it was made before being stored to improve it. You can also use vintage to refer to the wine that was made in a certain year.
eg This wine is from one of the two best vintages of the decade in this region...
2 adj Vintage wine is good quality wine that has been stored for several years in order to improve its quality.
ADJ n
eg If you can buy only one case at auction, it should be vintage port.
3 adj Vintage cars or aeroplanes are old but are admired because they are considered to be the best of their kind.
ADJ n
eg The museum will have a permanent exhibition of 60 vintage cars.
4 adj You can use vintage to describe something which is the best and most typical of its kind.
usu ADJ n
eg This is vintage comedy at its best.
Sourced - English Collins Dictionary - English Definition & Thesaurus
The admired part would be up to the owners I guess, lol. We know some bikes are complete shitboxes but they are included in fairness to the broader appeal they have eg Honda's, Yamaha's, Suzuki's and Kawasaki's lol !!!
Simple ain't it !!!
Dave Mac