abnormally

My 2.5 year old 3/4 Golden Retriever 1/4 Yellow Lab (his dad was pure golden, mom was 1/2 yellow lab & 1/2 golden) is 29 inches tall and 85 lbs. I know that he isn't a pure Golden, but even Yellow Labrador Retrievers average height is 23 inches. He is gorgeous but what could cause this? And...