Martin has said in interviews that he wishes he had made the kids a bit older; that's part of why they were aged up for the show.
Haha, it's cool to think that even Martin would agree with me in viewing the kid's ages in the HBO show as pseudo-cannon when reading the story.
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The Legend of Snake: http://tinyurl.com/3cal86z
The LoS Instruction Manual: http://tinyurl.com/3jlax8h