I've met a lot of young people who brag about "how mature" they are due to some life circumstances that have forced them to "grow up" fast... And inevitably, I find them to behave much less mature than those who admit to their immaturity.
I used to be a very active member of my city's BDSM "community" and I found exactly the cliquism GS was talking about. They also had an online forum, and I always found that any new people who didn't meet their criteria was ostracised and made to feel like a freak. That's exactly what you don't need when you're coming out of the closet and you already feel like a weirdo.
For the record, that's not the feeling I've gotten here.
As far as the age-marginalization goes, I think that's one of the benefits of the internet. To the extent that people are judged on their maturity, it's for how old they behave, not how old they are physically.
At 27, I'm right in the middle of the 18-35 range, and I don't feel marginalized at all. I don't feel the need for any special treatment. If we young people have any special issues or concerns, I'm sure that an open, welcoming community such as this is perfectly equipped to handle them...
I do not need a label to define me. Labels are sticky and I hate the glue they leave behind.