New cars are more efficient. As cars age they wear and become less efficient. Some cars as they get older leak fluids like oil and radiator fluid etc that contaminate the ground and although some people probably maintain their vehicles, i would suspect most people wouldn’t notice. Its also probably a good idea to steer people to newer cars for economic reasons too. So basically, older cars are more damaging to the road and environment which is why they should pay higher excise tax too

And lets get rid of manual transmission too