The owner has to complete and do certain tasks to earn points. When a certain amount is reached, the pet grows. The only problem with that is some owners will move to fast for the artists to finish their pets. If we use that system, we'd need some sort of road blocks.
Oh.
Then couldn't those just be normal requirements then? Rather than a point system.
It'd be much simpler to make it a checklist of things until the next growth.