Chesapeake Bay Retrievers

We have a chessie mix we purchased from a shelter in Feb 2011. Val still had puppy nails, had been neutered while pregnant (nipples were distended) and now the hair is growing white on her chin. She was covered with soft dark brown fur but it is more coarse and a little wavy now. The shelter guessed she was two in Feb but I think she's probably younger. Any ideas? How old are they normally when their chins turn white?