Kongs are a tried and tested favourite here at Your Whole Dog! I generally stuff with a quality canned dog food and freeze.
Here's what KONG has to say about their KONG Senior:
The KONG Senior dog toy is customized for an ageing dog’s chewing and play needs. The unique, natural KONG Senior rubber formula is designed for teeth and gums that have enjoyed chewing for years. Designed to provide a gentle and comfortable chewing outlet while offering enrichment and satisfying an older dog’s instinctual need to play. An erratic bounce makes it perfect for dogs that are still playing as they reach their more dignified years. To extend play time be sure to stuff with kibble and a dash of peanut butter. Your wise pup still looking for a mental challenge? Be sure to freeze for a longer-lasting treat.
Check the size chart to guide your selection.