[abaer]

The argument against this is simple. Rats and Humans are both mammals. Yet rats age an order of magnitude faster than humans, and they display precisely the same old age symptoms as they age. A rat is old at 2 or 3, and a human is old at 70 or 80. (Dogs and many other animals are in-between). This strongly indicates that aging is a biologically engineered process, optimized for each species.

That isn't to say there isn't some limit imposed by physics. Just that the limit doesn't appear relevant to what we call aging. The argument some have made below that physics imposes an age limit on a cell makes sense. Physics could impose limits on the lifespan of an organism’s replaceable parts — that could well be why organisms continually need to replace them.