Advancing technology is wing cars worst enemy.
I'm more of the notion that it's more the amount of time required to build rather than the driving or keeping up with the car aspect. It's a given, us old guys struggle with the speed but a youngster's eyes and reflexes are very able to handle the cars.
Case in point is my grandson, he's raced a total of maybe four times yet has done well in all four races, specifically at the 2007 Nats at our place last year (second place). Anyway, although he doesn't build, he was easily able to adapt to driving the car and was able to point out things that it was doing that I could not see. This provided me the opportunity to tune the car to suit him. I attribute some of this to the reflexes youngsters develop playing today's video type games and simply being young with eyes that actually focus and limbs that respond in a timely manner.
Unfortunately, I think it's hard to expect that kids today would be willing to spend the kind of time required actually building the toy cars before playing with them. Sure, there are exceptions but very few. Back in the "Day" we all built things, models, bikes, soap box racers, tree houses, etc., etc. I suspect many of our first cars were "Fixer-Uppers"; we either fixed it or continued walking. Not so much today, lot more ready to use stuff available and I find that kids aren't into the building aspect, maybe just my personal experience.