Well I have the 7 year theory....but its not bout cells. Its bout change. At 7 you start school. Then at 14 you hit puberty...which is another change. Then u hit 21...which again is sorta legal age. 28 is when u start feeling age. etc.

I know there is a bunch of loopholes but hey...u asked...this is my theory. :) It may not be a new you....but a slightly changed u...