That would be the longest hard working lab I have ever heard of. But its all down to how much work its had in its lifetime. Guys who work their dogs on 100+ retrieves, drills, plus miles of walking every single day are going to have the dog not last as long as the guy who just does a mile walk every few days and lets the dog run in a field some (upland hunting). The hips and joints simply wear out on labs, its not a breed that was built to run every day like some of the smaller pointers. My vet suggests starting on hip/joint supplements at age 3 for labs but there comes a point where the cartilage is just wore out and the dog cannot run miles anymore. Not a matter of being "in shape" or "fat", its a matter of the joints wearing out after so much use. Of course bad hips are an issue of their own within our breed, but I am not referring to those dogs.
Our furry friends have a milage rating and unfortunately you cannot replace parts reasonably.
I fully agree on the "build" of a lab and the concerns for the grounding and pounding they put on. Larger bone structure, larger muscle structure, broader build.....and they have the ability to put weight on quickly.
My Lab will be 8 in July. I have had him on glucosamine chews for some time now. I keep him on a good food. He gets zero human food/scraps. He gets about 2 to 3 miles of exercise a day. In the good weather months, on top of the daily brisk paced walks he swims a lot, way easier on their joints and stresses muscle groups not otherwise used. Plus, he is a Lab.......more like an otter in the water! I do as much as I can to keep him trim and well conditioned. His annual checkup in December, I had the conversation with my Vet regarding the "senior" stage beginning and food transition, if that was needed and such. The feedback I received was that my dog was in no way beginning the "senior" stage aside from his age.
I did GPS him once last year........was able to attach my FITBIT to him.......probably not the most accurate, but I use it and it's relative to the feedback I get when using it. My dog will typically range 15-20 yards or so each side of me, or the end hunter of a line and range 15-20 yards or so in front. If there is 2 of us spaced 20 yards apart, my dog is covering approximately 60 yards or so side to side and approximately 20 yards or so in front. So I figure he is always covering at least double or triple of what I am. The day I put the FITBIT on him, I did 6 miles on my phone, he did just shy of 14 miles on the FITBIT.
He gets watered with Kinetic Hydro 30K starting the day before hunts, during and after. I will give him fresh water too, but mostly on hunt trips he is drinking the Hydro 30K. I also supplement him with Mendota Health Aches/Discomfort tablets with his meal. He is rarely dragging his tail and is always ready to go the next day. He'd run himself to death if I let him. But on that note, rarely am I pushing him from open to close every day of a trip. There is always travel time, down time, stop and smell the scenery time, lunch, etc. Throw in those days of a quick limit too! LOL! I also don't let him jump up into the truck or down out of the truck either.
But like you stated above, I know that he is going to wear down more sooner than later, and sooner than some of the other breeds. It just is what it is with Labs.
Hey let me flash a point here I need a break! 
