[zxyzzxxx]

I remembered from school that the cell division limit is about 50 and evidence ( read: Wikipedia ) suggests that as well. https://en.wikipedia.org/wiki/Hayflick_limit

A tenth of a light-year is still impressive.

Even more interesting is the fact that the single cell organisms living in a human body, outnumber human cells by a factor of 10.

[astrodust]

There are exceptions, like immortal cells.

http://en.wikipedia.org/wiki/Henrietta_Lacks#Legacy