Ease of care
Senior dogs, in most cases, do not have the same exercise requirements as their younger counterparts. They have experienced the chewing/destructive stage long ago, and want nothing more than a warm pair of feet to lie by or a soft lap or couch to snuggle on. Their daily/weekly walks can be therapeutic for *both* dog and owner! Although some senior dogs may require more frequent veterinary visits, the joys of owning a senior dog will greatly outweigh the effort involved, as will the extra years of companionship gained.
 

Seniors for seniors
An attractive concept used by many animal rescue/humane organizations, an older dog can be successfully matched up with a senior citizen. Lifestyle requirements of an older person often mix well with the lifestyle of an older dog. It's a win/win situation, resulting in quality retirement companionship for both.
 
 
Who says you can't teach an old dog new tricks?
You sure can. While it may take an older dog a bit longer to adjust to new situations, they can; they will; they do. Their only requirement is to be given the opportunity. Generally, older dogs are calmer and therefore will focus much easier on what you are trying to teach them.