I got my second dog when Fig (my Boston) was 5 years old. She (Fig) did NOT like him AT ALL when I brought him home... however, she is very "alpha," territorial, and was not well socialized when she was young. She screamed and lunged at him and would have physically attacked him constantly if I did not keep them seperated. But after just a few days she warmed up to him (he's a hairless Chinese Crested) and after 3 years together they are buds. Fig still isn't his biggest fan, but if Tadpole (my Crestie) sneaks up next to her when she's sleeping, she won't get up and move and he gets to snuggle with her. :-)

I think it just depends on their personalities....

Gambit was really thrilled when we brought home a playmate, but after a few days he was giving us a look like "when is she going to LEAVE?"

Now that it's been about a year and a half, they get along fairly well. They still fight a lot, but at the end of the day, they go to bed snuggled up together.

However, we have found that Gambit, who had two years of being with people by himself, is very "mom and dad" oriented - he wants to be with us, and to play with us. Daisy, who never had that one-on-one time, is more "pack" oriented, and wants to play more or less exclusively with Gambit. So sometimes it's tough, because he craves one on one time with us that Daisy doesn't. So we try to make sure he still gets special time alone with us, while she's napping, to comfort him and keep that bond that he is so accustomed to.

They do fight quite a bit, but it's mostly playfighting. I think if your dog is comfortable with other dogs, especially irritating puppies, then it should be fine. Maybe try some social situations around smaller dogs and see what the reaction is? Gambit had seen and played with a few one-year old dogs before, so he was sort of used to little puppies biting him.

My first (Ziggy the grumpster) wasn't too much of a fan of Coco, my second. He was used to dogs so he didn't fight with Coco. But because he is such a dominant personality, he bosses Coco a lot. Coco doesn't mind because he is 5 years younger. When I got my third, Tito the Boston, Ziggy used to pick on him a lot but Coco was thrilled to have someone play with him instead of being a grumpster. They all get along okay. Ziggy still tries to assert his dominance by barking, growling, or lightly snapping at whoever is being insubordinate but they all cuddle together occasionally.

I got my second Boston when my first one was still just under a year old. I expected to bring home the new puppy and for the older one to be super excited and interested.
I was a little disappointed when the older one barely bothered with the puppy.
It's been about 6 months and now they inseparable.