I am house training an adult 3 yr old dog that has been allowed to use pee pads all his life. This handsome mix is a very shy boy and did take a day for me to be able to body handle him without him screaming. He is vetted and in good health, just has no idea where the toilet is.
Does Age Matter?
House training a new puppy or an adult rescue dog, uses the same technique, as you are assuming the dog has no idea where to eliminate. While you are conditioning a puppy a new behavior and your are counter conditioning an adult dog a different behavior needs to be considered in your time line for sure. Counter conditioning behaviors will most often take longer.