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In summary, "Oh dear, maths." Whitehound, who is meticulous about this sort of thing, has counted through the timeline presented in the new information, and found that - like with Dumbledore's age, where JKR spouted a number when put on the spot which later turned out to be unsupportable by examining details - Minerva McGonagall cannot be about seventy in GoF and therefore contemporary with Tom Riddle at school. Rather, she would be 58 or 59, thus 55 when Harry first sees her in PS (website says October birthday), with the black hair that people often use as evidence towards the "wizards age much more slowly" theory, and would have attended Hogwarts from 1947-1954. (Tom was 1938-1945 if I count right.)
It also confirms that Dumbledore was not headmaster when she began working at Hogwarts in 1956, rather that he was head of Transfiguration and she worked under him (i.e., it has not always been the case that there is only one teacher per subject; we have here at least one example of a less ridiculous number), which allows for him to be promoted between the time of Remus's infection with lycanthropy and his beginning at Hogwarts (to align with PoA where Remus says that at first it seemed he would not be able to attend, but the situation changed when DD became headmaster).
It also confirms that Dumbledore was not headmaster when she began working at Hogwarts in 1956, rather that he was head of Transfiguration and she worked under him (i.e., it has not always been the case that there is only one teacher per subject; we have here at least one example of a less ridiculous number), which allows for him to be promoted between the time of Remus's infection with lycanthropy and his beginning at Hogwarts (to align with PoA where Remus says that at first it seemed he would not be able to attend, but the situation changed when DD became headmaster).