It's funny that you bring this up, I was just having a look at this the other day... I have the answer for you.
Generally the Lexicon timeline is pretty accurate - as accurate as they can make it, and as accurate as anything you could find...
So anyway in 1997 (the year of his death) Dumbledore was 153, but we don't know what birthday is so it's impossible to say whether he'd had it that year or not. Dumbledore sat his NEWTs in 1862.
Griselda Marchbanks again on the Lexicon that she was probably born circa 1830... which means of course that at the time of Dumbledore sitting his NEWTs she was 32, and at the time of his death around 167.
But just to point something out:
DD is (or was) 150, right? and professer marchbanks exaimined him for charms and transfiguration, so assuming pro. marchbanks was 45 at the time, then she's 190! talk about old!
No way is she 190+. Sorry. Even by those stats there if she was 45 testing Dumbeldore for his NEWTs she would only be 180.