Scared Mastiff puppy

My wife and I purchased a full blooded English Mastiff just yesterday, he is 14 weeks old. My puppy was growing up with his two sisters and parents in a "run free" environment, and we have moved him to the suburbs. We have a decent sized fenced in yard, and plenty of room for him to explore. I know it takes time for an animal to adjust to his new owners, and environment, but he seems to be petrified of men, and is just now opening up to my wife. Is this behavior normal? How long does this behavior last? Not knowing if he sustained emotional/physical trauma by a man, will he ever open up to me? Any advice would be greatly appreciated.