One thing social networking does well is age your conception of yourself very rapidly indeed.
The ecosystem of social networking appears awash in ever-younger individuals, balding, increasingly frumpy strangers continually appear with familiar names stolen from the friends you had in high school, and you spend more and more time searching for the pictures you can post that show you "as you really are," rather than these oddly middle-aged photos that keep coming out of cameras that have been pointed at you.
Meanwhile, all of the people that you've known for years are too young and immature to ever cook their own meals and do their own laundry seem to be busy inappropriately having babies and working strangely exotic jobs all around the world as if they're actual regular, adult people.
This regrettable distortion of reality is made all the more regrettable by the fact that perfect sense can be made of the lot with an adjustment of the way you see yourself.
You say "God, I'm getting old, I think" and the pieces fall into place with alarming rapidity and clarity.