How long ago, and how far away, could "A long time ago in a galaxy far, far away" have been? Assume an event happened "A long time ago in a galaxy far, far away", and assume this event includes intelligent carbon-based life forms. What are bounds$^{a}$ on the time and distance (from us) of this event?
$[a]$ Bounds that take into account the history of our universe. I think the sentence infers that the event happened inside our past light cone.
 A: Only a partial answer, but:


*

*How long ago?  A prerequisite for intelligent carbon-based life forms to exist is that there are substantial amounts of carbon in the Universe.  This would probably limit us to some time after the Population III (ultra-low metallicity) stars burned out and the Population II (low-metallicity) stars took over.  It used to be thought that even the Population II stars didn't have enough "metals" for planets to form.  But the Kepler probe's results seem to imply that this is not the case;  there have been plenty of planets found around low-metallicity stars, it's just that they're not usually gas giants and so we hadn't detected them before Kepler was launched.
This gets us into the question of whether you need to have a gas giant in a stellar system in order for life to evolve.  It's been hypothesized that the influence of the gas giants in our solar system swept up a lot of comets and asteroids that would have otherwise impacted Earth and made things difficult for any proto-life.  So if you believe this, then you need a galaxy full of Population I stars rather than Population II stars, and the time window in which carbon-base life can exist opened that much later in the Universe.
Finding information on how long ago the first Population III stars formed, built up carbon & oxygen, and blew said carbon & oxygen into the interstellar medium is remarkably difficult.  I'm not an expert in the subject, but I suspect that it's not really known.  (With one recently found exception, astronomers do not claim to have ever observed a Population III star.)  These stars would have formed during the reionization epoch, which happened a few hundred million years after the big bang, give or take a factor of three.  Certainly by the time we get to 1 billion years after the Big Bang, we have a good number of Population II stars around, and we can't rule out carbon-based life after that point.

*How far away?  Given the answer to the above question, an age of the Universe of about 14 billion years, and the question's requirement that the events have occurred in our light-cone, then we're probably looking at somewhere within 13 billion light-years of us. 
