There are well over 100 different dog breeds and an almost infinite number of different mixed breed dog types. Large or small, long hair or short hair, high energy or calm and placid, mixed breed dog or purebred? It can all get a bit confusing if you're looking for a new dog, and especially if you're a senior citizen. I'll try to help sort out some of the factors to consider.
Some types of dogs may be more appropriate for senior citizens than other types, but the best dog for a senior citizen is the dog the senior citizen really wants. A strong emotional bond between the senior and the dog will go a long way toward overcoming some circumstances (such as size or energy level) that might otherwise be a bit overwhelming for the senior citizen. But in general, when deciding to get a dog, a senior citizen should take his or her physical condition into account.
Size
Dogs come in all sizes, from tiny teacup size (only 2 or 3 pounds) to bigger than a small person (125 pounds and more). Imagine the difference between having a 10 pound miniature Poodle on a leash and a 130 pound Mastiff. Although there are exceptions, in general a smaller dog would be much easier for a senior citizen to control.
Long Hair or Short Hair?
Many people fall in love with the beautiful long hair of a Yorkshire Terrier, an Irish Setter, a Golden Retriever or many other long-haired dog breeds. The coats of these dogs are truly gorgeous, but they can take a lot of time, effort and money with frequent brushing and combing and regular baths and trips to the groomer a necessity.
Now think about a "wash and wear" type of dog, one with a short coat such as a Beagle (or if you prefer a larger dog, something like a Labrador Retriever). The only grooming that's really required for this type of dog is an occasional bath (often only once or twice a year), an occasional brushing (maybe once a week) and nail trimming once a month or so. These dogs are just as loving, but much less time-consuming and less expensive too.
Energy Level
Everyone likes to watch an energetic, playful dog. They're fun to be around, but they can be a bit tiring too. A Labrador Retriever that wants to constantly play fetch (for hours on end) or go for 5 mile walks can wear a senior citizen out. So can a dog like a Jack Russell Terrier - lovely dogs, but they're almost always "busy" at something!
Some dogs just have lower energy and activity levels than other dogs. A "couch potato" dog - one who likes to relax and lounge about - would be perfect for many senior citizens. Older dogs are often more sedate than puppies and young adult dogs. Dog rescue groups and dog shelters are full of unwanted older dogs, so you might want to consider adopting one of these homeless dogs.
Your Dog Will Love You No Matter What Kind of Dog it is.