Lastest news is that Facebook has now outpaced Blogger as being the most highly used social networking tool (here). Even though Twitter is running at considerably lower numbers as a beginner, the general consensus is that it will soon dominate all forms of networking for business. Conversely, Facebook will remain the choice of many for networking among friends and family. But don't forget about Blogger. It will still remain strong in the general niche category, appealing to the broad public as a news source.
The truth of the matter is that folks will use social media as a combination (here) in different ways to create different social effects. The beauty of it is that you can become heard over night and in some respects virtually famous instantaneously (here). Or, just talk to yourself.
There is certainly a youthful demographic age bracket that uses social networking (here) but that is ever widening and in time will not be an issue at all. Let's face it, not everyone is completely sure how to use it (here) but the most important thing is that we are ALL learning, rapidly, and making it out own.
Digital social networking is not going anywhere.