I got Gracie at 7 months and she was used to a doggy door and piddle pads but she was pretty easy to train to go outside. We didn't have a doggy door then, we do now
But sometimes she still has accidents but not very often especially since we put in the door. I paid only $700.00 for her from a local breeder because she had floppy ears.
I weighed her 2 days ago and she was 4.8 pounds. I am still hoping she will fill out and weigh more but having my doubts. She just turned a year old on the 9th and has gone through her first heat. She is a very sweet, calm dog.
I don't think you will have any problems training an older pup as long as the pups has been in the breeders home and had some beginning training.