After their growth plates close. So 16-18 months, probably.
Non-forced running on grass is fine. Forced running on concrete isn't. The difference between the two is that on grass he can alter his pace, stop and sit, change directions, etc. It allows much more freedom of movement than running in a straight line using the same repetitive motion on concrete.
What else do you do with him to tire him out? Training sessions with mental challenges are a great way to tire a dog out. You could also look into a weighted backpack that he can wear while playing fetch.
I feel your pain. I have a very large and energetic Great Dane puppy. He's getting difficult to wear out. I just can't stress enough how much damage you can do to a young dog by running them hard on concrete. And with Danes, growth plate closure isn't until close to two years old in some males. So I've had to find different ways to go about getting rid of his energy. Might not be easy, but it's better than dealing with a 4-5 year old dog who is already arthritic and stiff because of joint damage.