Well. This is news to me.
Q: I've heard that every seven years, there's a complete turnover of body cells. If we keep getting these cellular 'makeovers,' why do we age?
A: Unfortunately, we don't get a 'cellular makeover' every seven years -- we just get seven years older. Different types of cells "turn over" at different rates. And some cells -- brain cells -- don't turn over at all.
I don't know when I first heard this notion, that the human body fully reproduces itself at the cellular level. When you think about it, it really isn't logical. But still, it's quite a romantic notion, anatomically speaking - the idea of being completely reborn every seven years.