Brief online debate between David Brin and Aubrey de Grey here. Brin points out that the low-hanging fruit for life-extension have already been picked, and that any life extension on the order of decades (not to mention indefinite extension) will require "thorough" intracellular nanotechnology. Agreed. There is always a component in every make of car that fails first, and even if you keep replacing components, eventually you'll be putting new parts in every day. This is why people don't keep repairing their cars indefinitely! What's more, a car is not a person. Your transmission is not you. Your brain is you. And we don't know how to replace that practically, and we still don't understand consciousness and self even at a basic philosophical level.
Living a long time is emphatically a worthy goal but we will not have this technology in the next few centuries.