I'm 23, living in the Bay Area (California), in a 5 year relationship with my "primary" (don't really like that word, but don't know what else to call him). I find that we're usually the youngest couple in the local poly community by about 10 years, which is interesting.
Big props to the moderator who posted in the community info that "poly is a fluid thing" -- I hate the narrow definitions of what it means to be polyamorous. Just like mono relationships have different boundaries, so do poly relationships. I would traditionally be identified as a "swinger" by the mainstream poly community, because my partners are primarily friends who become lovers. I tend to avoid heavily enmeshed emotional relationships. Just because I don't love everyone I see, doesn't mean I don't care about my lovers (which is what I think what "swinging" implies).
So, the childfree thing... I, for example, would not see another couple who had kids. A funny thing happens with poly relationships from time to time -- they blow up into a bloody emotional mess. I wouldn't want kids to be a part of that. I just find it incompatible with the lifestyle to have children.