Social media start-ups often seem to overlook an important demographic reality: age. These companies bet their business on behavior that works for young adults (say, 18 to 25), but may fall apart completely for people older than that.

Case in point: Geo-location applications. Maybe the business model for foursquare, Gowalla, et al. is a-OK with the idea of sticking to a younger set. Checking in where you are, and seeing where  your friends and relations have checked in, is kinda cool. Sprinkle in some useful information about where you are, and someone probably can make some money providing this service.

Of course, the thread that runs through that use case, and the product designed to support it, and the company built around that product, is the willingness to share information about your location. Pull out that thread, and the entire fabric of the business falls apart, unless it's designed to support only a small part of the population.

The Digital Age has been around for a while
The moment you look beyond that age cohort, you start running into problems. As colleague Dave Frankland discovered, the older you get, the less information you're willing to share. The reasons are rooted more in the realities of getting older than the effects of growing up in a digital age.

If you define Generation X as the people who are now 29 to 42, they already have grown up in a digital age. Long ago, they started ordering things on and heard how e-tailers collect and analyze information about you. They know that their ISPs have information about their web browsing. They lived through several generations of cyber-crime.

On the flip side, they've seen the Internet grow up, becoming increasingly useful with each generation of technology and capability. They knew what it was like to have a phone without Internet access, and they saw web publishing go from a dark art to something commonplace. They've seen the risks of the evolving Internet, but they've also seen its benefits. The Gen Xers probably take the positives less for granted than the generations that follow them.

Which is why it's important to note that Generation X's willingness to share personal information is less than Generation Y's. This cohort is hardly a group of fuddy-duddies, but they are the first step in a curve of increasing sensitivity to privacy, by age group.

The digital world has yet to replace real life
It's not hard to understand why. The older you get, the more focused you get on work. Your employer already owns a big chunk of your life, so why should they have potential access to information about where you've been and what you've been doing there? Also, a great number of life's landmarks, both good and bad, depend on a degree of privacy. The skunk works project you've doing for work, the trip to assuage the concerns of an angry customer, the romantic weekend get-aways (especially the illicit ones), the consequent visit to the divorce lawyer, the time spent in rehab, the visit to a friend who doesn't want everyone to know how sick she is…All of these events demand privacy, not disclosure.

Privacy is something that people want to control. A recent study by researchers at UC Berkeley and Carnegie Mellon showed how clear people are on the distinction between protecting your personal information and selling it. There is no "green field" of people who haven't formed preferences about disclosing their personal information.

If that doesn't convince you, here's another statistic that should shake your faith in the "Digital Generation" argument: the older the user, they more likely that person is to use online services to interact with government agencies. A young population may be steeped in digital culture, but they also have less reason to visit the city planning agency or the local IRS office than the older set.

Social media are revolutionary, for younger and older populations alike. Still, the next time someone tells you how earth-shattering something like geo-spatial apps will be, try imagining the twenty-somethings using it today when they reach their 40s or 50s.

[Cross-posted at The Heretech.]