This is the some of the oldest advice given when it comes to writing. It holds true even though it might feel a bit limiting, especially if to a young and/or inexperienced writer. So let me explain how I've dealt with this. Think about all the emotions you know. It's certain that you've experienced a huge range of feelings from euphoria right down to depression. Really explore those experiences. How did you move? How did other people understand your feelings or relate to you during that time? What were you thinking at that time? What made your emotion change? Then there are age issues . You cannot change how old you are, but in my experience the way you think will not change so drastically despite the encroaching years. What does change are your reactions to certain situations. (I find myself thinking, "Oh hell, I sound just like my mother." more frequently than I wish.) But anyway, there are always older or younger people around who you can observe. Look at
Musings on the mundane and the macabre and all the oddities in between.