When I was 14 years old, I ran a weekly D&D game with my friends and had to come up with stories--sometimes on the fly. The purpose of D&D is that you have a storyteller, known as the Dungeon Master, who narrates the story to the players. This includes the setting, plot, and non-essential characters. The players are the ones who tell the Dungeon Master what the essential characters do--and as any writer knows, your characters can often screw up your intentions for the plot.
I haven't been very active lately (busy with school!), but I have written a short post for the teen blog my library hosts. Check it out!