When an individual human grow from a fertilized egg to puberty, the complexity increases, it increases from a single cell to a body of millions of millions of cells with specialized tissues. It is a self-organizing process, more and more orders and complexities was established, and the entropy of body decreases during this process.
After puberty, at late teen ages, individual human body is stablized, and hence the body transition from a self-organizing state to a steady state. From then on, the body's complexity gradually decreases (due to wear and tear, or other reasons, aging), and the entropy of body increases, until the structure of body is no longer able to keep life stable, hence the increase of mortality and eventually death.
In the attachment there is a schematic diagram of change of entropy in lifetime, hence also the indicator of change of complexity/order.
The question is: why there was a turning point at teen age time when self-organization suddenly stops? Can we break this turning point, can we harvest the self-organizing power to prevent entropy increase? That might be a good way to achieve immortality.