When was that?

I'm not sure what you're getting at?

The way of looking at it was the way I compared my cat to me. My cat is 14. I am 35. Physically, my cat seems older then my 35 years, even though he is far younger. My cat is more like a person in their 70s, but he is younger than me - but I have a seemingly younger physique to him.

Same thing when you compare the Doctor to a human. He may be hundreds of years older, but his physical body appears younger. Its because his species is longer-lived than ours. For him to live that long, his body is going to take a long time to "decay." It needs to be resisting the physical affects of aging, otherwise it would fail much sooner. Consequently, it will look young until it starts succumbing to the affects of aging. As soon as that happens (and the affects become visible) he is going to be approaching the end of his life.

Maybe before he was using his last bits of regeneration energy to slow down the ageing process then either before or during Time Of The Doctor he ran out completely.

but you keep comparing two different thing's which I'm not. I'm saying as many other's have - period before wedding of river song, hundred's of years, not a day older in apperance. Time of the doctor, hundred's of year's, lot's of difference, even if you only look at the half way point when he was only slightly older looking (which was probably more like the time scale for period before wedding of river song). Not different species aging being talked about here. one character, one body, similar scenario twice different outcomes of aging

it's entirely possible, but as it stand's from what were told on screen, it's another one of those moffat era thing's where you have to (as you have done) try and make it make sense yourself, as the actual episode's don't give any indication of the truth.

They did show slight signs of aging during his tenure such as him needing to wear reading glasses in Angels take Manhattan.

Matt himself talked about how he had started getting grey hairs during his time on the show and he certainly does look older in Series 7 than he did at the start of Series 5.

So he ages about 300 years with some slight signs of aging but only looks really old after a further 900 years of aging.

yeah but that was aging over his whole tenure, for it to make sense he would have had to look slightly but noticeably older in closing time than he did in the god complex, as it was set 200 years later from his point of view

You seem to be missing my point of comparing how species age. You seem to think that he MUST look physically older because he'd aged 200 years during his "farewell tour," in the latter part of series 6. I'm saying that for a species that can last 600+ years in a single incarnation, aging 200 years is probably much like us aging 5 - 10 years.

There's no reason his body is going to decay in 200 years if he's still got 400+ years of life before he'd reach a natural death. Look at it like that; those 200 years might be the equivalent of a human's life between 20 and 30 years old. He's not going to show much in the way of physical signs of aging. A little, of course (and Matt does look older than he did in 11th Hour), but nothing significant.

You wouldn't look at a human and say "oh they haven't aged much between 20 and 30," then look at them again between say, 60 and 70 and go "wow they've physically aged a lot. That doesn't make sense because they didn't age that much between 20 and 30."

That's the reason I made the species comparison. My cat has physically aged more than me in 10 years because his species is shorter-lived. The Doctor ages less in 200 years than we do because his species is longer-lived. But just because his species is longer-lived, it doesn't mean he won't start to age and decay as the centuries pass by - just like how it doesn't mean I won't eventually get old and wrinkly just because I'm longer-lived than a cat.

There's absolutely no issue or contradiction in the Doctor not aging much in the first "missing 200 years," and quite visibly aging in the first 300 years of Trenzalore and then again even more so in the unknown period of time leading up to the end of the episode.