You can start from very 1st day at your home...there is no proper age...it's exactly how we train our child that how to sit, how to behave, what is allowed and what is not and what is good or bad nothing else. Just remember one thing that they don't understand long conversations and will never...use short words only like 'Yes,No,Come,Go, Sit with gestures and when he/she do that appreciate with a kibble.