In one scene of the first movie, Sally recalls as far back as 40 years earlier, when things were different. Although we don't see her in the flashback all other Radiator Springs folks are there and don't seem to be that young already.
Forty years ago, that Interstate down there didn't exist. Back then, cars came across the country a whole different way. Well, the road didn't cut through the land like that Interstate. It moved with the land, it rose, it fell, it curved. Cars didn't drive on it to make great time. They drove on it to have a great time.
— Sally Carrera, Cars (2006)
So how old are they actually?