I've read that labs and pits are two of the healthiest breeds, and that mutts are healthier than purebreeds, and he's all, three, so apparently he's going to live forever.

I wasnt going to say anything for fear of coming across as a snotty, snooty purebred fancier (I love mongrels equally...hell, I AM a mongrel of mixed heritage) but this is a fallacy started by Don Burke, a celebrity GARDENER here in Aus (the guy wouldnt know a bush from a tree) who had a huge legal battle with our kennel club because they wouldnt recognise his
designer mutt so he has spent years trashing purebreds, and he loves throwing around 'hybrid vigor' to back himself up. Dogs are mammals, not freaking plants. I loathe that arrogant tool - more on him later. And a UK nutbag 'animal rights' activist who made a doco about ill purebreds at Crufts, and used dogs not even in the dog show as examples. She came onto the aussie purebred forum I told you about, Yods, and got completely annihilated. That was fun.
Saying that, however, it;s great your dog is healthy. And beautiful.
I dont know what it's like in USA but here a lot of genetic testing is done and results given to buyers in their puppy package. Selling a defective 'product' here, which is how they're seen in the eyes of the law, can get very pricey for registered breeders, but not the ass hat backyard breeders and puppy farmers because they dont register with the canine council so there is no fall back. I had my show dogs hip and knee xrayed in the unlikely event I would ever breed them, but I retired them and had their bits fixed, and never bothered sitting the exam to become a registered breeder. Too much crap to pick up, too hard to sell the puppies, didnt want to deal with tools wanting to buy - long story, and got sick of the bitchy show world. My jack breeder was my mentor and when she died I lost heart.
Herein endeth the lecture. Getting off my dog geek high horsey.