Your level has nothing to do with your entry to Marleybone, young Wizard.
Once you have completed all your required assignments in Wizard City, Merle Ambrose will ask you to investigate Krokotopia. Once you have been given that quest, you can access the Spiral door by entering Bartleby the World Tree.
After you’ve completed Krokotopia, you can move on to Marleybone, then MooShu, then Dragonspyre. You can visit Grizzleheim at level 5, but cannot return until level 20.