When I first heard about PvP I had been using my troll hunter, and decided to try it out. I think she was around level 28-29. Note that I had no idea what PvP actualy stood for a the time. All I knew was that it gave honor, and you could gain ranks from it.
I was in Stonetalon and flagged myself then killed that level 30 Gnome with the lantern that is right before Windshear Crag since it said he was "PvP". I looked in my honor log and wondered why I didn't get anything for killing him. So I turned my flag off, waited for him to spawn, and did it again. After the third time, my kills stayed at 0 and I went to the WoW site to read about PvP. Then went "Oh" when I discovered you only received honor for killing other players, not the NPCs.