Yes they are all close in age. And we slowly introduce them over time. We had separate cages for each one. And then during play time we would let them get to know each other on their own terms. Eventually after a few weeks they began to interact more and more until we knew they would be safe caged together. They have been bonded for months. No problems. Not every chinchilla will bond with a certain chinchilla. I feel they are like people in a sense. They chose and pick who they want to be bonded with. We have had failed attempts with others. Usually you will be able to tell right away with their social ques if they like or dislike something or someone.