Frankly, I suspect the premise is right. As a retired person in that referenced age group, and also active in WOW guild activities, I think the challenge of both problem solving and socializing keeps me connected.
On the other hand I'm egotistical enough to think I fall into the group whose cognitive function was already high, so I don't know that I can say it has IMPROVED my function significantly. Helped maintain, yes. Improved, doubtful
A shot in the back saves nine.