Your Body Is Younger Than You Think (2005)

Ignoring these surface cells, the average age of those in the main body of the gut is 15.9 years, Dr. Frisen found. Dr. Frisen has found the heart as a whole is generating new cells but he has not yet measured the turnover rate of the heart’s muscle cells. About the only pieces of the body that last a lifetime, on present evidence, seem to be the neurons of the cerebral cortex, the inner lens cells of the eye and perhaps the muscle cells of the heart.

Source: www.nytimes.com