That isn't what I'm saying. When I hear teens and college students talking bad about Facebook, they aren't mentioning old people (though that probably is the root cause), they are saying Facebook by name. They are saying "Facebook sucks" not "Old people suck, old people use Facebook, ergo I am declining from using Facebook for now until I too am an old person".
It sucks because you can't freely post anything there, without people (family / coworkers) judging you. I don't want to broadcast to that group of people. If I need to talk to them it's personal or in small groups, so that's done in instant messengers.
The only people I would like to broadcast to are close friends or strangers on the internet.
I don't have that many close friends, so a bigger IM group is enough for that. (I guess Instagram might work if you have lots of "close" friends.)
That leaves only my need to anonymously talk to the internet. So Twitter, reddit, personal blogs?