Also anecdotal, but...
As I started getting into heavy research on recommender systems for our startup after being somewhat lax in my research reading for a few years I stumbled into some papers that were really hard for me to push through. I kept thinking, "I must be slipping, I know this stuff wasn't as hard for me in college."
Then at some point I needed to look up a couple things in some of my textbooks (I saved them all) and as soon as I picked them up I thought ... wait? That was the hard stuff? This is all so ... trivial. Since the progression from textbooks to academic papers had mostly come at some remove, I'd not noticed that I was gradually reading much harder material, to the point that the stuff that I found hard in computer science in college now seems all rather easy.
Now, I'm 28 at this point, but already I've noticed that I'm not as fast as I once was, but I've got more momentum. When I throw myself at a problem it's with the goal of crushing it rather than dancing around it. This seems to be what's awesome about smart folks that are in middle to older ages. There's like this blunt force of knowledge that can be thrown at hard problems. Great systems programmers in their 50s are awesome to work with.
Note, also, that the article also mentions that knowledge based abilities increase up until you're 60.