I stumbled across the following interview from J. K. Rowling the other day while perusing the questions on this site, and came across the following question:
Will there be, or have there been, any "late blooming" students in the school who come into their magic potential as adults, rather than as children? By the way, I loved meeting you, and hearing you speak, when you came to Anderson's in Naperville. I can hardly wait until you tour again.
Ahhh! I loved the event at Anderson's. It was one of my favorites. That is completely true. No, is the answer. In my books, magic almost always shows itself in a person before age 11; however, there is a character who does manage in desperate circumstances to do magic quite late in life, but that is very rare in the world I am writing about.
My question is, which character is J. K. Rowling referring to? I don't seem to recall any characters getting their magical powers late in life (granted, there are characters like Neville whose powers take some time to truly 'mature', but that doesn't sound like what she is referring to).