Hi, I'm glad you are enjoying the game :)
55 is default level cap. You can increase it: in Path -> Sow Seeds add points to Wisdom Level Cap and Rebirth.
Another way to increase it is through the "Tier" Milestone, no Rebirth needed.
You can check you level cap in the Qualities -> Extra panel, "Wisdom Level Cap".
Let me know if anything requires further clarification :)