I don't think I can put my finger on a definitive age demographic. I think it's just certain types of people with whom I get along better. They however, quite often end up in a certain age range.
For me personally, I tend to get along fine with people who don't take life to serious and like to take a chance in life every once in a while but at least are aware of what's going on to some extent. I guess one could call them the "irresponsible" adults. That might just as well apply to myself.
A few years back, I regularly visited a local gaming store (cardgames and such) and while I was in my late 20's, the majority of the folks there were between 15 and 23. I didn't really have a lot of issues with those people in general. Yes, there were exceptions, but everyone has some people he/she can't get along with at all. Some just were full of antics, and nothing but that... and I'm convinced it was attention seeking for a big part. But I managed fine with that group of people there (even though I didn't go there to socialize, but to play cards, I still had a chat here and there). That crowd in general wasn't overly serious in life and just did whatever they wanted to do. And I guess rightfully so at that age. You would notice a big difference in between the crowd from the ones that were in school (or just dropped out) and the ones that had a full-time job. It's behaviour, appearance, amongst a few other things. I've dealt better with erratic behaviour that borders on serious issues (and had the most wonderful conversations with these people) than I did with people who actually took life serious and were geared towards a stable future. Perhaps I just have a thing for all things broken.
I notice patterns from time to time in the crowds I hang out with. From all the people in my social group, as well as those in the past, I never got along with anyone who was employed. Perhaps that's the "irresponsible" part in me. And the ones that were employed had a weird deal going on. Like a childhood friend of mine who basically runs a 1 man gamedevelopment company pretty much from his bedroom. And while I don't want to discredit him and his job, it's not a job in the traditional sense. And looking at the "older" folks I end up chatting with at times; it's the type of people that run their own tattoo parlor or thriftstore. So that's probably not the most traditional form of employment. They might be a bit more responsible though, heh.