Is he really a purebred Golden Retriever?

I work at a doggy day care and see a lot of Goldens. Quite a few of them have black spots on their tongues, so that doesn't mean anything. There are plenty of dog breeds with that. His size is quite large, as you said. I have never heard of or seen a Golden getting that big. There is one Golden at daycare who is about 130 pounds and he is one of the most overweight dogs I have ever seen. His health is failing because of it too, poor guy. But it sounds like you have some kind of mix. There is a way to tell. You can get his DNA tested and they can tell you what he is. If he is pure golden, you probably have one for the record books, but I kind of doubt a pure Golden will get that big. Maybe there is some mastiff or dane in him.