One of the reasons we sometimes hear association and corporate marketers use for hesitancy in incorporating Facebook into their communication strategies is their perception that it is comprised primarily of college-age students. That's correct, however, the trend is clearly in another direction.

According to this analysis of current (September, 2008) users of the social networking service from O'Reilly Media, "With the U.S. now accounting for only about a third of all Facebook users, we are starting to see a gradual shift away from its original demographic of college-age users (18-25): 46% of all users are 18-25 years old, down from 51% in late May. The number of users in the 18-25 segment is growing, but at a slower pace than the other age groups."

More significantly, Facebook is seeing its fastest growth among teens (13-17) and middle-age professionals between the ages of 35 and 44. Also showing strong growth, but at a smaller rate are the age groups 45-54 and 55-59.

Should be interesting numbers to track.