I noticed that now that I'm at a higher level (23), when I go back to some of the earlier maps (e.g. Brackenridge), it says it's a No XP zone. I assume that means I don't gain any exp points by running this map.

But, my PETS were still leveling in those maps.

Is that ALWAYS the case? Or, once the pet reaches a certain level, do they stop gaining XP on lower level maps, too?