I remember a time when I was a child and wasn't aware of what happens as we get older and older. I asked mum what happens afterwards, and she said we stop getting older and older, and start getting younger and younger until we are children again. Then we get older and the cycle continues. I thought it was a beautiful thing and looked forward to my "second" childhood.
Today I acquired a unique perspective on how the above metaphor is exactly what happens with our germ (egg and sperm) cells. In the lineage traced back to the beginning of time, one cell never died. It grew forwards and specialised into the cells that make up a new individual, including that one germ cell that was passed on. At fertilisation, the cell started going backwards and turning into a totipotent stem cell that could once more grow forwards and specialise again. To germ, back to stem cell, to germ and back again. Backwards and forwards, backwards and forwards. Never dying. This cell has been alive for all of time, and is now alive within you.
So when you think what a "long" life should be, think of how long this little fella has been around.