Young Balls are very effecient at getting the most from their food, especially if the food item is on the small side for them. It's nothing to be concerned about as it's not uncommon for them to go a couple of months without defecating even though they eat every week. Just make sure he has a clean supply of water and be thankful you don't have to clean up stinky cages that often. Oh, and they typically go right after a shed...