It may be the case that the slowing down isn't just offset by gains in knowledge, but caused by it. That has some exciting implications for the quality of results from older hackers!
"A series of simulations show how the performance patterns observed across adulthood emerge naturally in learning models as they acquire knowledge."
"A series of simulations show how the performance patterns observed across adulthood emerge naturally in learning models as they acquire knowledge."
http://onlinelibrary.wiley.com/doi/10.1111/tops.12078/full