Are old cars carbon footprints different from new cars does the footprint become spent after a period of time?

The carbon footprint of a car is primarily its gas use efficiency meaning the number of miles it will travel per gallon of gas. Since all cars, old and new, burn gasoline and produce carbon dioxide to move the car, the more miles you get per gallon translates to fewer gallons of gas used to move the car. This applies to straight gas cars and hybrids (not plug in hybrids) since they all get their primary energy from gasoline.