fictional character from Harry Potter
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Dumbledore was approximately 150 years old when he died, according to J.K. Rowling.
Question: How old is old in the wizarding world, and how old are Professors Dumbledore and McGonagall?
J.K. Rowling: Dumbledore is a hundred and fifty, and Professor McGonagall is a sprightly seventy. Wizards have a much longer life expectancy than Muggles. (Harry hasn't found out about that yet.)
Scholastic Chat - 10.16.00
I'll add this from the Harry Potter Lexicon, which addresses the fact that Dumbledore's age seems to be less than 150 at the time of his death:
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 [Skeeter] 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.
Harry Potter Lexicon - Albus Dumbledore
Basically, it boils down to JKR is really really terrible at her math!
The HP Lexicon lists Dumbledore's birth date as either July or August 1881 and his death as June 1997 so he was 115.
I dug a little more and found this from JK Rowling's Wizard of the Month posts from her website. The site no longer has the article but I have summoned it back with the Wayback Machine.
Albus Dumbledore
1881 - 1996
Brilliant and often controversial headmaster of Hogwarts School of Witchcraft and Wizardry, Albus Dumbledore is most famous for his 1945 defeat of Grindelwald and his steadfast championing of Harry Potter, the Boy Who Lived. Dumbledore's self-proclaimed proudest achievement, however, was featuring on a Famous Wizards Chocolate Frog Card.
I have a theory that Dumbledore was friends with Nicholas Flamel and maybe had a few elixir "drinks" with Flamel from time to time. Perhaps Flamel would gift a small bit of the Philosopher stone and Dumbledore would make it into a nice cocktail drink.
At the time of his death, Flamel was over 665 years old, and perhaps drank the elixir every day, whereas with Dumbledore, it was more of a "life-boosting" occasion.
Theories?