Professor Marchbanks was the witch in the council which has visited Hogwarts in the OOtP for the OWL tests.
She was once quoted saying:
... not if Dumbledore doesn't want to be found! I should know....
Examined him personally in his Transfiguration and Charms when he did NEWTs ......
So, she was one of the examiners back when Dumbledore was giving his NEWTs.
And owing to the fact that Dumbledore is considerably old by the time Order of the Phoenix happened, I guess she must have been at a pretty impressive age for a human being.
So, is there any close-to-accurate calculation on how much her age can be?