every 7 years

They say, and when I say they, you know who I mean, that every cell in your body regenerates itself every seven years. Yet you are still you. You can look at old photos of yourself or even perhaps a baby picture, and somewhere inside yourself you know that is you. I've been thinking about that recently and what it means to me.
As I wrote before, while in Japan I've fallen in love with cycling and yoga. Somehow I just can't picture myself ever not doing those activities. Yet as recently as three years ago, I wasn't doing either. It's funny how we change and do become new people over and over again.

Recently, I watched the the movie Eternal Sunshine on the Spotless Mind which deals a lot with memories. Basically, the premise of the movie is that there is a process in which a person can erase all the memories they had with a certain person or animal or whatever. They wake up the next day and don't remember ever having a relationship with this person.
Anyway, I've been thinking about memories and time and as I choose certain times in my life to think about I've found that I can create a picture of myself in that time, high school for example, but I have a hard time remembering exactly what I was doing or how I spent all those days. I find it hard to create more than glimpses of moments into my life then. Strange.
Sometimes I find my life in Japan to be as surreal as recalling any of these memories. I wonder if five years from now I'll be able to think back to my life in Japan and remember it anymore clearly than my life in high school.