"STORY SLAMS" are usually more urban, avant garde, and definitely adult venues. They are edgy, progressive, hip-hop inspired short stories told in fast forward of the experiences of modern life. Think storytelling counter culture or the tales of a new, different generation being spun in ways previous tellers might never have dreamed. They are often held in coffeee houses, museums, art galleries, night spots, or city parks. There are, however, events aimed at teens and young adults (see http://www.youthstorytelling.com/toolbox/Youth_and_Storytelling_Keding.pdf)
There is a very good blog at First Person Arts that includes a description and a video. These are operated a little differently and have emerged from the "Poetry Slam" movement of performance art. They are often competitions and regularly tellers put their name in a hat or jar and the lucky ones tell. There is one that occurs in OKC - usually in June - check the MySpace page for insights: http://www.myspace.com/okcstoryslam.
An article in the New York Times from 2001 provides another view: http://query.nytimes.com/gst/fullpage.html?res=9C04E2D61038F933A25754C0A9679C8B63&sec=&spon=&pagewanted=2 ;