I have saw some strange (at least strange for me and my knowledge about the game) pets with level 50, here's one example: 

http://beastkeeper.com/pet/35333

from what I see, the pet doesn't have a lot of fights won (either on arena and on battlefield), doesn't have a lot of islands visited, and doesn't have a lot of quests completed - so how is it possible that it has level 50? are there some more ways to gain levels I'm not aware of? or I just don't see all of his characteristics because I'm not the owner?

thanks in advance,

visenna

You can train your pets with a ridinghall.

hehe, oh my! sure! I forgot about it! thank You!

locking

Also: Experience can be gained by fighting monsters and gaurdiens on the islands, experience halls on the islands, quests and crafting. :)