Drivers need to be mentally very tough because the pressures places upon them are immense. They are constantly being measured against the other drivers of course but also against their engineers' expectations, not to metion expectations of sponsors and owners. I don't think a driver has to be extremely bright, not a slam, but you can't be an ignoramous either. Because if you are already in your 20s it is too late. No one starts playing basketball in college.
Most top racers start as teenagers at latest.
An exception is Damon Hill who didn't enter his first car race until he was 24, but he was a motorcycle racer before. We just did a story in Automobile Magazine about kid racers and Jimmy Vasser and Richie Hearn started when they were about six and eight, respectively. Clearly the more manufacturers there are the more opportunities for factory-based teams, but I don't know what effect this will have at this point. When you are 16, believe it or not, you can start racing professionally in some states. We'll see when F1 comes to Indianapolis.