I doubt you'll get much more than speculation on this one. There's far too much timey-wimey bullshitty-wullshit in Doctor Who for it all to be reasonably said. That said, here's some speculation :-)
I'm going to quote a block of text from the wikia (emphasis mine):
Even without regeneration, Gallifreyans had considerable lifespans. Within one regeneration, Gallifreyans could live for hundreds of years, yet look much younger than a human of equivalent age. When artificially aged 500 years, the Fourth Doctor looked like an elderly human (The Leisure Hive). During his eighth incarnation, the Doctor spent over a century trapped on Earth and never seemed to physically age during that time. In his eleventh incarnation, the Doctor looked essentially the same for two centuries, (The Impossible Astronaut) though at least three more centuries caused him to age somewhat and six more centuries of further time caused him to age into a very old man, near death from old age. (The Time of the Doctor)
However, Gallifreyan children grew at about the same rate as humans of the same age. (The Sound of Drums) After this point, ageing would slow, with the Gallifreyan looking like a teenager for decades. The Tenth Doctor referred to himself at ninety years old as being "just a kid". (The Stolen Earth)
The Second Doctor once stated that, barring accidents, his people could "live forever". (The War Games) The Doctor once said that he considered himself at approaching 750 to be middle-aged. (Pyramids of Mars) One Time Lord, Quences, was killed when he was over 7,000 years old. Professor Chronotis suffered from senility when over 12,000 years old, and the Eleventh Doctor showed some signs of the same on the brink of his thirteenth and supposedly final death at "over 2000" years old. (The Time of the Doctor, Deep Breath)
From this it sounds like ageing works differently according to a Gallifreyan's position within their lifespan. We know for sure that when they're young they age like humans, and later on their ageing slows. The evidence in your question suggests they age more quickly towards the end of their life (or maybe towards the end of each regeneration, if they regenerate due to old age?) as well as the start. This would explain why the Doctor didn't age in The Impossible Astronaut but did in other episodes, each time shortly before regeneration.