I must have got real lucky with my 8 year old boy. He's extremely food motivated. Made training a sinch. Sometimes I put a bit of warm water in his kibble to make a gravy and eats it like its his last meal.
I used positive reinforcement with my service dog Ringo. He is 8 years old (been training him since he was 1) and is peaking as a medical alert dog. There is no such term to us as "Training is done"