Training an older dog requires some accommodations, but it can be done!

There are a number of factors that influence how much and what your mature canine pal can learn, including:

Your dog’s training and behavior history. If your dog has learned how to enjoy learning and is engaged in an ongoing training program, he will continue to learn easily. Studies show that humans who continue to exercise their brains stay more mentally alert than those who do not. We have every reason to believe the same is true of dogs.
Physical conditions that limit his mobility. It seems obvious but we’ll say it anyway: If your dog has physical limitations, he may not be able to perform new behaviors that require physical exertion. Joint or muscle pain, arthritis, hip dysplasia, obesity, and heart problems are some of the more common physical conditions that can interfere with your elder dog’s willingness to try some new “tricks.”
Also, get an okay from your veterinarian before enrolling your senior dog in a physically vigorous training program.

Your skill as a trainer and commitment to your dog’s training program. They can’t do it on their own. The better you are at communicating to your dog – reinforcing appropriately and in a timely manner for desired behaviors – the easier it is for him to learn new behaviors at any age. The more consistent you are about working regularly with your dog, the easier it is for him to learn, no matter how much grey hair he has.
What you are trying to teach him. If your goal is to change behaviors that your dog has been practicing successfully (getting reinforced for) for a decade, your challenge will be greater than if you’re simply teaching new behaviors. Changing long-held classically conditioned (emotional) responses is likely to be more challenging than teaching new operantly conditioned responses, where the dog deliberately chooses behaviors in anticipation of reinforcement.
What methods you have used – and are using – to teach him. There is overwhelming anecdotal evidence that dogs trained with positive methods are quite willing to keep on learning – while those trained with physical and/or verbal punishment are more likely to shut down and less willing to offer new behaviors. If you want your dog to be an eager participant in the learning process well into his sunset years, be sure to stick with a positive training program.
Mental conditions that limit his cognitive abilities. Canine cognitive disorder, sometimes referred to as “Doggie Alzheimer’s” is a very real phenomenon. Clinical signs include those changes owners often refer to as “senility” such as: disorientation, “acting old,” increased sleep (especially during the day), altered interactions with family members, loss of housetraining, decreased ability to recognize familiar people and surroundings, decreased hearing, restlessness, decreased desire to perform favorite tasks (such as walking), standing in the corner, and barking aimlessly at inanimate objects.

Canine cognitive disorder can significantly limit a dog’s ability to learn, although there is a medication approved for this condition (Anapril) that can often alleviate symptoms.

To conclude, training an older dog requires some accommodations, but it can surely be done!