I had the privilege of flying with a pilot in his Mooney starting when he was about 70 and continuing for over a decade. He was a charismatic, lively man and a good pilot who had been flying since WW2. We flew together several times each year for proficiency and breakfast runs.
His skills did not appear to decline steadily. Instead they seemed to occur all at once, in a step-like manner. The steps happened several times over a decade.
Outside the cockpit he was the same warm, intelligent and articulate man as always. From the right seat, though, the steps were glaringly apparent.
His stick and rudder skills seemed unaffected; so long as he was in VMC he always flew well. The deficits were cognitive. In one “step” he seemed to lose flows and checklists; the checklist was still in the side pocket but he no longer remembered them, and he no longer realized that he should use them. Another step was a large reduction in situational awareness. Flying in the area where he had lived his entire life, except for his war years in the Pacific, he had no idea where the airport was. Not only had he lost SA, he appeared to have lost the very concept of SA.
In none of those “steps” was he aware that he had lost anything.
I know that one example doesn’t make a proof. I also know that my own body is neither as strong nor as flexible as it was ten or twenty years ago. I would prefer to think that my mind is not similarly weaker, but there’s little reason to think so.
I suspect that the actuarial data for driving a car are relevant to the more complex tasks of flying. The more limited data from aviation suggests that is true; older drivers and pilots have more incidents and accidents.