What Jo says about...
Minerva McGonagall

Please note: unless you see quotemarks, these are summaries, and not JKR's words themselves. Please see the linked article for the actual text.

• The MoM does not find out which children are magic. Instead, there is a magic quill in Hogwarts that records the birth of a magical child, and McGonagall checks it every year, then sends owls to those magical children who are turning 11. [Read the exact quote from Scholastic chat #1, 2000]
• Under her "gruff" exterior, Prof. McGonagall is an old softie, really. [Read the exact quote from Scholastic chat #2, 2000]
• McGonagall is 70, and Dumbledore is 150. Wizards have a longer life expectancy than muggles. [Read the exact quote from Scholastic chat #2, 2000]
• If a teacher is head of a Hogwarts house, we can assume they were in that house. [Read the exact quote from Jo's website]
• Although McGonagall is a worthy second in command, she is not Dumbledore's equal. [Read the whole quote from the Leaky Cauldron, 2005]