Who did magic late in life in Harry Potter and the Deathly Hallows?

JKR said (in an interview after PS and before CS) that one character in the series performed magic relatively late in life. Obsessive fans and fanfic writers had championed various Dursleys, squibs and Mary-Sues as candidates for this role, and were disappointed when DH didn't provide any obvious answer. The most straightforward interpretation of JKR's comment is that it referred to Neville, who only exhibited magical prowess when thrown into water by an uncle, at eight or so. Magical ability in the Potterverse seems usually to manifest itself in the under threes; an eight year old without signs of magic would be a desperately late developer. The relief for Neville and his family would have been commensurately huge. In an interview a few days after releasing Deathly Hallows, Ms. Rowling said she changed her mind and did not use this in the book after all.