As far I know the body is a machinery that is constantly replacing and creating new cells. Some cells death while other new cells are created. Each tissue has a specific life so bones, skin, etc.. are constantly being created and destroyed.
Aging can be seen as a degeneration of that process. I mean, from newborn to sexual maturity ~20 years, the body is in an anabolic state. After that, the body is on anabolic process that little by little shows the signs of aging.
Well, I think that aging can be seen as a process where the regeneration mechanism is being discharged. By discharged I mean a process that is being performed less and less perfect and complete. There is "something" that get exhausted and finally the body cannot me managed and it dies.
That "something" could be an electrical process, something like a quantum non-linear process that is directly related with DNA activation. That energy could come from oxidative processes and those oxidative processes are more and more inefficient in time because some basic substances get finished.