Old people homes, that's not the same thing. I've heard of what you're talking about, but it's not the same community you get in college.
As for retireds/middle aged people, they have no community whatsoever. They might be able to fly out to Vegas or something, but that's not what I'm looking for. I'm looking for the drunk hookup upstairs at a college house party that everyone came to because college is the kind of community where news of a party travels. I'm looking for living in a dorm, and then getting invited to the girls' floor because they like me. I'm looking for that stuff you see on Do It For State.
After college, this all stops. That's why there's so many articles and whatnot trying to help people make friends when they leave college. Because the dynamic changes. There's no community to make friends in or have casual sex in. It's all co-workers and people on the train and strangers on the street. Who you could maybe end up having sex with, but it's not a community. There's no one to turn to and say "I'd like to have sex with So And So from Such And Such." There's no classmates to lust after and talk to your friends about and have them tell you stuff about her. I could go on and on about the stuff college has that real life doesn't have.