Adopting a new, older mix and my JRT

Hello
I've had my EJRT Rudy (he is neutered) for a year and a half now. He is very sweet and friendly and I'm thrilled to have him.

However, for some time now I've been thinking he could benefit from having a friend in the household. I volunteer at my local SPCA and have been keeping my eye out for a good playmate and companion. I recently found an older, female dog that is extremely friendly, great temperament and loves dogs, cats and kids. She is spayed and is between 7 and 9 years of age but is still playful even though she is quite calm. I'm thinking that she might set a good example for him.

I know that she will be a wonderful addtition to my life, but how accepting will Rudy be? Although he can be submissive with other dogs, he loves to play and I think this dog might fill a void that I cannot.