If you look at the GM quests on the calander most, if not all, the GM's will put a level limit (essentially to keep the challenges from getting stupid-hard for anyone below that) Or a level minimum (To keep you from getting massacred due to the stipid-hard challenges)
Unless specifically stated +/- Level 'X' ONLY You are welcome to join in, but if you join something with a large group of high level characters you will be taking your life into your own hands.
Have you searched around for the NPC quests on Mistone? Theres a lot of them, and they provide ample challenge to the beginning adventurer.
Vyris