Deciding WHEN to get a puppy.

Good Morning everyone. Me and my wife are thinking about getting a puppy for our 3 1/2 year old son to grow up with. Currently we have a 9 year old boxer/pit mix (Koda), who is the most well behaved dog I have ever owned. We ended up getting him from a friend of mine who had too many dogs about 5 years ago. Right now, we don't really want to have two dogs in the house, but could manage. I have heard that puppy's tend to learn from other dogs when they grow up in an environment with another dog, unfortunately dogs don't live forever, and our boy Koda is getting up there in age. I kind of of want to get a puppy to live along side Koda, to learn from him as he grows up. What has been your experience with having a puppy living alongside your older dogs, as compared to raising your puppy alone? is there really any benefit to having another dog around for your puppy to grow with?