As Facebook’s numbers continue to grow, a huge shift in the site’s demographics is underway. According to StrategyLabs,  who have archived data provided by Facebook through it’s self-serve ad system since 2007, the six months from January 2009 to June 2009 saw the addition of almost 5 million new users aged 55 and over.

The rapid growth of the platform may have led some of the first supporters of the site, college and high school students, to abandon it for greener (and younger) pastures. The newest data available shows that self-identified high school and college students’ numbers have dropped by 16% and 21%, respectively, and growth for the 18-24 segments have slowed to a trickle of 4.8%, compared to the rapid expansion of the 55+ segment, growing at an astounding rate of 513% over the same 6 months. Some marketers might be left wondering where all the kids have gone.

Facebook boasts 71 million US users, and continues to grow in every age demographic. The 18-24 set still accounts for 25.1% of all users on the service. However, only six months before that, it was 40.8% of all users. Some caveats are that Facebook’s numbers are rough, and there exists some possibility of fewer users self-reporting their school affiliations or that a saturation point has been reached for younger users.

However, it is more likely that the aging trend will continue, and the audience of Facebook will grow progressively older. This presents new challenges, but new opportunities as well, to appeal to an increasingly tech-savvy and more sophisticated older consumer.

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Originally posted at Speaking of Social Media.