Novelty Toys
Some dogs prefer toys that roll, as they like a long chase, whereas others prefer toys that are shaped to bounce erratically as these simulate the twists and turns of live prey. A game of hide-and-seek with his favorite ball or toy is a great at-home game for your senior dog.
Another idea is to make him use his "sense of smell" by developing a game of "Search and Rescue" which all dogs seem to love. Pick out an object such as a dog treat or toy. It's important that you allow your dog to thoroughly smell it. Make him remain in position while you hide the object. Now, tell him to "find it" and watch that nose go. It might take a few times for him to catch on, but he will.