Absolutely correct re the exercise while still a pup, don't overdo it according to our vet.
To show another side, our 7 YO Chocolate Lab is a dream regarding exercise and chewing. I always felt (and still do) a bit uneasy about leaving him all day, 8 hours, on his own in the house....while its far from the best thing to be doing, he does'nt bother too much, never chews (apart from a rare bit of mail) and seems to just be a lazy house dog. A dream with the kids, you can play fight, he'll never bite too hard (soft mouth)....and if you get the chance, take him to water. I've never had a dog that loved the water that much, rivers, streams or the sea, he just loves it.
Mine does have bad hips from a year old so we were always told don't exercise him too much so while he goes nuts if you get his lead out, we don't over do it, you can see he's tired after a mile at the most.