I would not take him for consistent running exercise yet. Is there any way that you might find puppy play groups in your area ? They do power the little ones out while they give them the option to rest up in between romps. It also does wonders to their social behavior.

Especially a large breed dog has to be handled carefully in that regard. Also, don't underestimate brain work. Working the pup twice a day for short periods of time in obedience will tire them out too. Another thing you could do: get dog games like buster cubes or or games where the thinking process of your dog gets challenged.