The common definition of antique is a collectible object such as a piece of furniture or work of art that has a high value because of its considerable age, yet it does in fact vary depending on the source, product, and year.

Motor vehicles are an exception to the 100-year rule. The customary definition of antique requires that an item be at least 100 years old and in original, unaltered condition—which excludes most cars. Therefore, cars are generally considered antique if 25 years old or more. (Cars can be registered as "classic" when 20 years old.).

These definitions were intended to allow people of that time to distinguish between genuine antique pieces, vintage items, and collectible objects. The alternative term, antiquities.

Source: Wikipedia