The definition of plateau is reaching a state of little or no change after a time of activity or progress. Once this happens you need to change the course, find something different, another challenge, change up your training. Your body can continue to improve, it just needs to be challenged. Your balance and strength must be challenged if you want them to improve.
No matter what they say about old dogs and new tricks there’s something called “Neuroplasticity”, which is the ability of neural networks in the brain to change through growth and reorganizations. Just like your muscles the brain can be improved and change itself to function in a better way by simply challenging it.