It looks like he aged, but we don't have any solid info about the intervening time.
First off, yes: the image in the mirror is a younger version of John Hurt, produced digitally from footage of the actor at a younger age.
We do know that Time Lords age, slowly but surely. The primary use of regenerations is to stave off the effects of aging; the Doctor's unusually exciting life means that he rarely gets the chance to grow old, but that's just one of the many ways he's an atypical Time Lord.
However, going by on-screen information (and anything which isn't broadcast on screen during a proper episode of Doctor Who is of questionable canonicity at best, and will likely be contradicted by "screen canon" later), we just don't know much about what happened to the War Doctor during the Last Great Time War. The Time War undoubtedly lasted for a very long time, in a wobbly kind of way, and he was probably there for most of it, but we don't have any specifics.
Alternately/additionally we could speculate that he got caught by some kind of "aging attack" at some point in the Time War (perhaps similar to the effect the Master used to turn Ten into the Dobby Doctor), but there's no concrete support for such an idea.