I think a normal human lifespan, on an ideal wild raw diet, barring early death from violence or infection, is probably around 120-140, with the absolute upper limit around 180 or 200.
On the other hand, with the use of certain meditation or even alchemical techniques, I think the practical limit is much, much higher. Granted, there's a lot of BS surrounding all this, but I've seen some things that have opened my mind, so I definitely at least think some of this is possible.
With advanced science, including stem cell research, I don't think there is any real limit to human lifespan. In fact, I'll go even farther and say we'll beat the aging process altogether within 30 years. This is assuming, of course, no major natural disasters, accidents, or terrorist attacks that would kill a large portion of humanity.