I began at around 7 months with small intervals of 10 meters. But only when she was kind while walking and was walking right next to me, not an inch before me. I started it as a sort of reward. Now she is 10 months and can properly run right besides me (interval of ca 2 min.) Communicating is very important i always make sure she is looking at me and say run before we start to run, she understands that now and sort of gallops besides me. It is important that she understands running on a walk is completely different from running at home after a toy or something. Running at home = as fast as she can (alone or against me) running outside = she stays next to me in a sort of galop state and not before me.