How Old?

So, how old are you anyway? When asked of a person, the question really means "How long ago were you birthed?", but the question has some other interesting elements as well.

The essential 'me' might be considered to be my mind, and thats probably been around since not long after my birth, albeit in a more primitive form. But my mind is always changing. A mind is a river, changing in every instant, and yet recognizable through time.

But my mind is a part of my body; how old is that? Obviously some parts are new, the skin is renewed quite frequently for example, while others are mostly 'original equipment', the brain comes to mind, so to speak. But are those cells really new? The come directly from other cells, leading all the way back to a single cell with my genetic makeup. And even that cell, with the exception of half its instruction set, a fairly small part of its makeup, came from some other cell. So the cells making up my body have a lineage that extends all the way back, presumably, to not only some of the very first cells on Earth (and if you believe in panspermia, possibly even from Mars or another distant body), but to pre-cell formations. Somewhere in the distant past a few organic molecules came together in a configuration that happened to be self-replicating, and from that event an unbroken chain of replications hundreds of millions of years long leads to directly to me.

So how old am I? In a sense, I am new in every instant, and yet I am also hundreds of millions of years old.