Considering adopting- Please help

We are thinking of adopting an older 치와와 from our humane society. they think he is 12 years old. He came in as a stray.His discription says he's a sweetheart. I wanted to know what older chihuahuas are like, and just anything in general, such as are they easy to houstrain? Are they calmer 또는 friendlier, and how well do they get along with other dogs? We are buying a 강아지 다음 summer, so do 당신 think the 치와와 would be okay with that?