We have only had him for a few days but appears to be potty trained and although cautious seems to get along ok with our Boston Terriers. I know very little about chihuahuas but he seems pretty laid back and I would guess he is a young adult. He has yet to bark and prefers to be in the same room as humans. He is not jumpy but will show his teeth if he gets scared. We don't have kids or cats so those are both unknowns.