The phrase of something being a lifetime ago exists for a reason.
You're changing mentally and physically all the time, especially when you're younger and going through so many phases of growing up.
String enough of those changes together and at some point you will effectively become a new person, only connected to the previous iterations by memories that you share.
The death of one interation and the beginning of another is bound to be a blurry mess, but you can see it clearly over a large enough span of time.
The same is true with the environment around you, and even the wider world. It goes through iterations just the same as we do because nothing stands still, even if we want it to.