But don't worry; if your older dog is peeing in the house or pooping in the house you probably still can housebreak your dog. (Hey, just last week I taught 14-year-old Karl to shake!)
Many older dogs that require house training come from adoption agencies. They are unreliable in the house for one of two reasons; first, they never were housebroken (which may be why they were put up for adoption in the first place) and second, they were housetrained but for some reason forgot how they were supposed to act.
If the older dog were given insufficient opportunity to relieve itself outside, it may have just gotten into the habit of "going" in its kennel.
However, unlike a puppy the older dog has established some habits that will have to be "unlearned". So patience in housetraining your older dog is a virtue.
When the dog is in the house with you do not let her out of your sight! If necessary crate her, tether her near you with a 6-foot lead or use children's gate to keep her in the room. Be proactive in your housetraining and eliminate the opportunities for mistakes.
Take him to his potty area first thing in the morning, last thing at night and several times during the day. When he "goes" lavish him with praise—that's the most important thing to your dog. If you'll be away during the day consider crate training your dog.
House training an older dog should not be difficult and success should come relatively quickly. Mature dogs have better bladder/bowel control than puppies and they're smarter; to quote another worn-out old adage, "With age comes wisdom." And I'm banking on that being true!