There's something to be said for having a lot of shared history with a person. There's a level of comfort that cannot be reached without the passage of time. The type of conversation and recollection of memories is so much richer if you've known a person through many stages of life.
This is how it is with Amy and myself. It was so great to catch up and just talk for hours with her. She will always be a good friend of mine and I feel like we are getting to a similar head space. We're definitely in different phases of life (I think she's overtaken me in the growing up process), but there's more common ground than there has been in the past.
It's so nice to have friends with whom you can grow and change, but still be reassured that they'll always be there.