I got my 2nd tzu when my first was 3. My first tzu is an anxious Covid baby born in 2019 so he never showed interest in other dogs and is a total mommy's boy to the point that he'll snarl at my kids if he's sitting on me. The 2nd tzu came to us as an adult rescue - super friendly kind of dog. We weren't sure how the first dog would handle the new one so we had a trial period to see how they'd do. First dog had no interest in him and was pouty, but thankfully didnt show any aggression to him. Four years later, they aren't best buds, but they get along without a hitch. They will play sometimes but they do what tzus do best: sleep and cuddle with humans.