As dogs get older, they may develop age-related health problems such as arthritis and joint and mobility issues, restricting what and how much activity they can do.
You'll likely need to slow down and maybe limit the distances you travel when walking your pup. Your pets decline in levels of activity may not always be related to age. Keep an eye out for subtle signs of pain. If you're worried, you can visit your veterinarian so they can come up with an ideal treatment plan.
A dog's sense of smell continues to remain sharp in old age. You can use this to both your advantage by playing scenting games with them to keep them entertained and mentally and physically stimulated. There are several indoor scenting games you can play with your pet.