Well, to a certain extent.  Some body part transplants have fairly high success rates these days, such as the liver, lungs, heart, and eyes.  But what about the brain?  The brain literally defines the person as who they are, complete with memories, a life lived, skills acquired, educational levels, etc.   If you replace that, has not the person ceased to exist?  Not to mention that successful brain surgery, at least in terms of replacement, has yet to be mastered.  So I think life can be prolonged, to a certain extent, but when it comes to certain critical parts, such as the central nervous sytem, there will still be a "stopping point" in terms of a human life expectancy.  Humans, like every other living thing, have a reasonable life expectancy within the parameters of their species.  The average life span of a human now is well into the seventies.  Other organisms, such as the fruit fly, have a life expectancy of a few days, while some species of pine have been known to exist for thousands of years.