Nascar, I suspect (as with Aussie Supercars) would have athletes driving them. Supremely fit, well tuned and highly trained athletes for the sport in which they compete.
Very true however as you say that Motorcycle racing has few 40+ people riding professionally but that is more a side effect of the sport than showing it as requiring superior athletic abilities than does car racing. Many motorcyclists retire (sorry KJD/Dubs [emoji14] ) before 40 due to ongoing injury but they often still compete, just maybe not at the top level whereas Car drivers maintain the extreme fitness and are competitive at the older age.
In Oz V8's, there are drivers who would be as fit if not fitter than many motorcycle racers if you measure their fitness for their sport, not as a direct competition for the other.
...., if darts players are athletes (and officially they are), then sure as .... sticks car racers are athletes