If your dog is aging and is having mobility issues, adding a hip & joint supplement won't hurt and is absolutely worth a try. However, when dogs reach a certain age and are limping a lot, a majority of the time they will be in need of stronger medications, such as arthritis medication or prescription anti-inflammatory medications.
Unfortunately, there are no over the counter pain relievers available for dogs like there are for humans. Do not give your dog ibuprofen, aspirin, or Tylenol, as those can be very toxic.
Limiting walks and play to 10 minutes a day will help with limping, but visiting your vet when you see these symptoms is the best course of action.