Your parents are obviously still fairly active, and this means that most small dogs, as apposed to toy dogs, can be included. I would discount most of the obvious choices of medium breeds, such as the Labrador, since these benefit greatly from a lot of exercise.

Most of the spaniels would require a lot of grooming, especially if they are going on lots of country walks, and I guess being near a golf course you also want a dog that can be trained and will generally be well behaved. My suggestions would include a wire-haired border terrier or a cairn terrier. You may find that terriers have a reputation for barking, but these two breeds you will find very reserved and amicable even with most other dogs. I hope this helps.