12-year-old dog trained me at age 39
We took one of our Shelties to SPCA-sponsored obedience classes at age 12. I agree with what other responses say, that Shelties are smart enough to learn at any age. The biggest advantage for Nestle was the mental stimulation from learning new things and getting treats for it! There were some behaviors that we let go for two long, but for the most part her anxiety level went way down because I learned how to be the "alpha dog" in the family. She stopped lunging at strangers, pulling on her leash, and started listening when we told her to leave things alone. All of this was for her own health and safety, and for my sanity. Obedience training is the kindest thing you can do for an adult dog with behavior issues.