Running With A Puppy

I have a 5 month old 12 pound Mini Aussie pup with lots of energy. I am wondering when it is OK to take him for regular runs with me. I have taken him a couple of times on 4-5 mile trail runs at a slow pace (9-10 minute miles). He runs ahead, stops, runs ahead, etc. My vet said to wait until he is 10-12 months old for sustained running but this doesn't seem very sustained to me. When we get home he tears around the backyard and looks forward to playing hard with the neighborhood dogs. I am wondering if this is OK or if I really need to wait until he is older.
Thank you.

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