Based just on age, the gap is (arguably) zero.
BUT attaining and maintaining the required level of fitness becomes exponentially harder. Especially if you’re driving shifters. Ironically that’s why I went road racing because I wanted to race shifters, but the required fitness was more inline with my, eh… abilities. I’m not implying that you don’t have to be fit for road racing, but it’s easier to be in the hunt and survive the weekend if you’re someone that’s not pounding laps and a gym on the regular.
Remember that fast driving is more about programming and planning, less so reflexes.
If you want to go down a bit of a rabbit hole in heart rate, we’ve got you covered.