OK. Here is my theory regarding the Doctor's age.
The Doctor refers to his age in Gallifreyan years and Earth years. Hence how he can be 1000 in Sylvester McCoy's era (he celebrates his 1000th birthday in one of the audios, so he must be at least around that age in the TV series), yet have de-aged to just over 900 in the recent TV series (and that gradually increases to match the length of the new show).
As for why? Well, it makes sense he'd use Gallifreyan years when Gallifrey is still there and he's a proud member of an existing race. But once Gallifrey has gone and he's the last of his kind, referring to the time scale of his lost home planet would bring up bad memories, so he switches to his 'other' home world, Earth. It also means he freaks out his companions a little less, though admittedly 900 isn't all that much better than 1100 (which he must be by now, surely).
Anyway. As for the whole Golum thing... Time Lords physically age much, much slower than humans. It's how they live so long. The Master basically took that away from the Doctor, making him look his 900 (or 1100, whatever) years.
Think of it in human terms. If we live to be 100, we get smaller and more wrinkled, right? What would happen if we we kept alive till we were, say, 200? How much smaller and wrinkled would we look then? We'd probably look like
Hans Moleman. Apply that to Time Lord standards, and we get Golum.
There. Now be quiet and give me my God-Damn No-Prize.