(Spinoff of my own from the "Things you should stop doing by age X" thread)
I dislike the idea that adults should segregate by age. It doesn't seem in keeping with how we're made (you couldn't have your thirtysomething group in caveman times; not enough members), with charity, or with dignity. That's one thing I like about the Knights of Columbus, ManKind Project, and I'd hope other fraternal orders are the same: your age group is "man." Not another limitation: you're too fill-in-the-blank; go away. We wouldn't do it on race; why age?
But if I think about it, part of me also wants to segregate by age. I'm late 40's. I wouldn't just hang with the college crowd. Or the retirement center crowd. And I must admit, it's for a very American reason: I think the college crowd wouldn't want me (youth is superior to age) and I think I'd find the retirees dull (youth is superior to age, again). Isn't this wrong-headed? (The Chinese would think so; they value age over youth, so I hear.)
Or is it true? At my college one of my students told me to come down to the college ice-cream study break. It wasn't weird because I wasn't there as an equal, just a professor dropping by for free food. But I found their conversation (movies, music, books) more interesting than I do that of those in my age range. Maybe we do get dull as we age.
We naturally segrate by age.
But it's usually not just by age. It's often by age and circumstances.
An example would be the "progression" young males and men through the church groups I've observed in my parish.
First you have the teen group, whose members then find themselves in a "Singles" group, which when then they've married, and the children arrive, it's "Lifeworks", followed by PTA and the cubscout/campfire girl parents, then "Sports Boosters",
I agree with Native Son. It's not so much age as life-stages. I think we all need activities in our lives that have a mix of both.
It is REALLY HARD for me to stay friends with my age-peers who are already married and have children. I think they talk too much about diapers. They think I talk too much about work. But to be whole adults, I think we need to be forced through those conversations.
OTOH, we need friends in our lives who share our biggest interests, which will usually be tied to our life stages. After all, half my married-with-children friends work, it's just work isn't the same priority for them as it is for me.
Super-girly example: "Meet other brides" is a common retail event recruiting strategy. The idea is that friendships of pleasure can be formed. I don't get it, personally. Why should the mere fact we're engaged simultaneously and live in the same region make me friends with someone? But other women gobble this stuff up.
I can believe it, and yet I don't think I fit in with my cohort. OK, so I know few men with small children. But I'm uninterested in talking with them about it. Maybe an occasional joke, but... diapers are boring.
Maybe I'm antisocial, or maybe I just never grew up.
Diapers are boring until someone starts wearing one on their head...
I've gotten to see some of this dynamic at the parties of someone I know: the hostess invites a great range of people, including in age. I seldom see age segregation going on; with a bit of alcohol, some fun things to do (adult twister and contra dancing) soon everyone is talking together.
Outside of a party situation, yes, It think we do tend to segregate, though for an introvert like me it means segregating myself from everyone, age doesn't matter.
Age may be a factor but I think it has also a lot do with personality, interests and all these things that are part of friendships (or at least mantaining relationships). I'm not particularly close with some people in my class but I do have an easier time talking with some adults I know from somewhere else. One of the most interesting persons in my class is around 6 or 7 years older than me and he is a very interesting person. But classifying and segregation is just part of human nature, I think, just like we do with everything because we like order and we like things to make sense to, at least, the majority of people.