
Originally Posted by
The Lexicon
Minerva McGonagall
JKR said in Sch2 that McGonagall was "a sprightly 70" years old. Using that information, we can determine the year in which she was born by subtracting 70 years. As with [Dumbledore]'s birthyear, the trick, of course, is knowing what year to subtract that 70 years from. If we assume that Rowling was saying that McGonagall was 70 years old at that point in the stories, which was summer of 1995 [[Y15]], then she was born in [Y-55] ([Y15] minus 70 years). According to the official timeline, [Y-55] is 1925. Interestingly, that would make McGonagall a contemporary of Tom Marvolo Riddle at Hogwarts...
Albus Dumbledore
Birthdate: 1881 (JKR), probably in July or August. This date supercedes Jo's statement in 2001 that Dumbledore was "about 150 years old" (Blue Nose Day) and fits better with the dates that appear in Book 7. Regarding his month of birth, Rita says that Dumbledore was “nearing” his 18th birthday when he left Hogwarts in June, but was still 17 when he met Grindelwald (DH18). Basically, at some point during Grindelwald’s stay at Godric’s Hollow Dumbledore turned 18, so the month of his birth appears to be July or August.
First year [at Hogwarts]: 1892.