What this really shows is that developers get better at answering technical questions with age. There is probably _some_ correlation to development skill, but the data doesn't demonstrate that. I'd expect developers to know more things as they get older, and I wouldn't be surprised if they got better at answering questions. Not sure that makes them better at the development part.
I think that this is showing a correlation between those programmers that enjoy programming and want to share their knowledge with others, and those programmers that stick with it for more than a decade.
I bet that if you could separate out the younger developers who will still be developing in 10-20 years, that their rep on SO is similar to that of older developers. Those developers that'll wash out in the next 5 years are dragging down the participation numbers of their peers.
So it isn't the age that's important, it's the personality type which is correlated to those people that'll stick with development.
Since programming is a skill based on the technical information, and since practice/experience is even more important for skill development than for other types of learning, I would expect their abilities to be even better than predicted by a test of their knowledge.
