I know it is easier said than done, but I would not worry. They will end up getting along fine. Just takes a little while for them to get use to each other. I was majorly worried when I got Zoey about 6 weeks ago. I don't have any other pets other than my 9 year old Yorkie who has been spoiled like no tomorrow and was use to all my attention. Although I take her around other dogs and stuff, I always joke that she has no idea what to do with other dogs. She never really learned how to play with them and thus really just turned her nose up at them and tolerated being around them for a short while. So, yeah, was very worried. When I first brought Zoey home, she flat out ignored her. And I mean literally would turn her face the other direction when she saw her. Then she got to the growling phase, even nipped at her a couple of times BUT amazingly she never was really not nipping hard. She knew she was just a puppy. Zoey would even go when she was chewing on her rawhide and chew at the other end and she would just growl, but still let her do it. From Zoey she is slowly starting to learn to play like a real dog now too.
She does get a little tired of Zoey because she is so energetic, but she does play with her and has become protective of her. So trust me, if a 9 year old dog can get use to a puppy, yours will too. Give them both lots of treats as rewards at the same time and praise them both together. If your dog sees it is still getting attention too it will be more accepting.