It happens to everyone as they grow up. You find out who you are and what you want, and then you realize that people you've known forever don't see things the way you do. So you keep the wonderful memories, but find yourself moving on.

This quote is talking about growing up and having different experiences from the people from your past. As you grow older, you develop a stronger sense of who you are and what you want in life. As a result, your views may be different from the views of people you’ve known for a long time. Even though you will have many great memories from the past, you will likely find yourself needing to move forward and pursue your own path.