While easily replacable brain matter is a step in the right direction, more is definitly required to extend avarage lifespan. Dying of "old age" usually consists of major organ faliure. This is not just completely natural, but pre-progemmed into our DNA; it's designed to shut down the organism after its normal lifespan. By the nature of cell replication, each cell generation becomes progressively more mutated, making it more difficult for the system to operate, exacerbated by accumulated damage from the environment, such as radiation and smoke inhalation. If the body let itself get as old as possible, it would literally be asking to become a carrier of cancer and disease, as the mutated immune system would barely be able to function.
So if you want to live to be two hundred, cell rejuvenation would probably be the way, along with a few other theoretical processes. Always nice to be better able to repair our brains, though.