There are many things that affect our driving and flying.
Being careless while young is one issue, and some states are looking at
changing the minimum age driving rules because of this.

But sticking to the issue of ageing..
There are different problems with flying and driving. Driving a car is
easy; dodging all the idiots, in what amounts to a trip-long reaction
test, is not. Think of all the signs you have to sort out, intepret,
and react to at some high speed. Look for lights, kids, cars, bumps,
brakes, cops, snowballs, etc. What you need to know to drive is
minimal; what you have to do at all times is incredible.

Flying is itself harder, but that is possibly compensated for by much
practice. You have to study and learn a lot, and it can be hectic near
an airport from time to time. But generally, it is calm and it's
usually not a reaction test. You have a lot to do, but that involve
radio, navigation, and other such things as can be practiced. You
don't have traffic lights (once up and away), too much traffic to
dodge, signs, tailgaters, and the whole host of perils that exist on
the roads. You really don't have to worry about nearly as many
airplanes hitting you as you do cars. When was the last time you heard
of a 90-airplane pileup on the runway?

And while there are some boneheads amongst us pilots (you all and me
excluded, of course ;) ) I generally like to think that pilots are a
bit more courteous and attentive than the average car driver.

When I get as old as I plan on, I intend to keep flying. I may make
the decision to fly only with an instructor or other qualified back-up
pilot in the right seat, just in case. I'd still be the pilot, I'd
still be flying. Perhaps a requirement similar to this on a
certificate is appropriate (Ho jeez, I hope the FAA doesn't see
this--yet another regulation.) Airplanes have another advantage
here--you usually have dual controls; cars never do.

I am certain that drivers who age and lose their ability to get around
by car on their own still have to be taken out from behind the wheel.
Our society doesn't deal with this very well, since we seem to reject
mass transit and prefer jammed roadways in celebration of "freedom?".
We also seeem to think that "respecting" them means allowing them to
do whatever they wish, regardless of the dangers to the general public
and themselves. I don't think we take this attitude with any other
identifiable segment of our society.

But I'd sure hate to get wiped out because some person of advanced
experience couldn't get to a brake pedal on time, and we let them
continue to drive just to make them feel independent.