How can you understand if your Golden Retriever starts to get OLD ???

I know that many of you guys know how to understand it but for the people who doesn't know, I'm sharing this information. 

   The fur on his/her face gets lighter. You can see it better if it's a red/dark yellow type of Golden Retriever.

   It's starts to move slower so you shouldn't take him/her for too long walks because its heart can get tired easily. Just like an old human. 

   

   P.S; I know some old Golden Retrievers which are 11-14 years old , they still move fast and they're still energetic. That means it's really healthy. But you still shouldn't make them tired or shouldn't play fetch for too long times. So it's energy mustn't trick you.