There are various dog breeds that you could pick from for instance: Yorkshire terrier, cocker spaniel, pug, Boston terrier or a miniature or standard poodle. The smaller breeds with low energy levels are recommended for old people.
Interesting question; I used to do home care for seniors and they seemed to prefer smaller dogs, but there's a very elderly man in my neighborhood who has a standard collie (like Lassie) that he walks daily. I would suggest a breed with a lower energy level, which would leave out most terriers and poodles, imo. I tend toward the larger breeds, so a Great Dane, a St. Bernard, a greyhound (no kidding) or a mastiff would appeal to me. Smaller breeds that have a calm reputation are Pugs, Japanese Chin, Bolognese, and Chihuahuas. They all require minimal exercise.