The signs of a golden retriever starting to become sensible include being obedient, well-behaved, docile, recognizing the road, recognizing its master, being clingy, acting coquettishly, and helping others with things, etc. Golden retrievers generally start to become sensible after one year old, so this is the best training period and can also help the dog develop good habits. Golden retrievers are the smartest when they are about four years old, and training will be more effective. Easier.