Access to the worlds of the Spiral is not dependent on your level, but on the quests and assignments that you've completed. Once you've completed all your assignments in Krokotopia, you will be invited to explore further in Marleybone.
Its not of level. Its by the quests. once you finish krok,krokosphinx and then you get to chamber of storms then you get to go to marley bone. The last part of krokotopia is Defeating krokopatra so if you have that quest you know your close