The Great Pyrenees I have seen that were herd guards were all around 150 lbs (not fat), or more. Usually male. I would assume a 100 pounder to be a youngster or a female.
He could have weighed that. He probably did, I was only guessing, and not trying to over guess.
Great family dogs
My sister gave him to some sheep ranchers. He was just too much dog for them.