Although, there used to be a definition of vintage as being 21 years old (or maybe it was 25) for Road Tax purposes (ie, anything older than that would be exempt), but this was stopped for any vehicle built after 1974
According to my insurers a car must be 30 years old to be described as 'Vintage'. This is normally decided via enthusiast clubs and insurance agents. So call your insurance company and ask them.
If your car is a collectable or quality car it would be a Classic car. It would not be a classic purely because it was built before 1973 though, whatever the insurance companies say.