http://cs.unm.edu/~aaron/blog/
By looking at the game histories of each of our participants, we did discover several interesting age-related patterns. First, unlike the stereotype described so vividly in Gus Mastrapa's Wired Magazine article "21st-Century Shooters Are No Country for Old Men," older players are, in fact, better at the game (kills per game) than younger players, and this is especially true for the team-oriented players.
Suck it, teenagers.
Age does seem to correlate with the preferred style of playing, with younger players (slightly) favoring the "lone wolf" style. This supports one popular perception about younger players, but it turns out that younger players are not actually better at this role than older players (see the previous figure). That all being said, most players (almost 80%) prefer team-oriented roles.
There you go... scientific evidence.