So I was looking at the AH and saw a level 20 pet for only 600g so I managed to get it. But now it says that it is too high level to uncage. My highest level pet is only 14 at the moment. Must I level my own pets to 20 before I can uncage this one? If not then what is the requirement?
Yes you need to have a level 20 pet in order to open a level 20 caged pet. Slightly related: do not ever cage your highest level pet if you can (asuming you only have 1 pet of this level) I have heard of people who was set back by 5 levels and more because they caged their only high level pet.