I attend (sporadically) the Seattle Modern Quilt Guild. I'm by no means the oldest person there (mid 40s), though I would say that the majority are in their late 20s or early 30s. It's not so much an age issue as a sensibility/taste in quilting, with a lot more emphasis on improvizational techniques, non-traditional patterns, use of modern fabric lines and designers, a graphic feel to the quilt design.
My experience has been that older/more experienced quilters are generally welcomed, though be prepared for a new generation of quilt police ; ) -- some of the younger quilters who have learned via blogs or new quilt teachers can be just as vehement about their ways as any old school guild member, and ironically enough, over some of the same issues, but on opposite sides of such compelling and divisive topics as --seams, press them open or together? Templates vs. rotary cutting? Organic cottons only? -- just for the hot button issues I heard discussed.
RST