Although the terms for cars vary, especially if you look at insurance sites, cars can be classified as "classic" or "vintage" before they reach "antique" status.
I think this Wikipedia entry does a good job in giving an average standard, citing the Antique Automobile Club of America's standards as cars having reached 20 years as being double their design life, 25 years as "vintage", over 45 as "antique".
In general I think with most items are considered "vintage" at 50 and "antique" at 100 years of age. Cars are the exception. (Someone correct me on this if I am off-base please.)