Comment: Professional Graphologists - like the ones that work for the FBI

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Professional Graphologists - like the ones that work for the FBI

would say that you can't be 100% certain of the author's age or gender, but you can guess with some degree of certainty based on a couple of things, such as the 'slant' of the writing. To quote from Handwriting and Personality:

"Multiple slants are common in children's writing before the age of fifteen, partly because the extensor muscles in their hands aren't fully developed. Sometimes, however, multiple slants occur in the writing of children who are being emotionally pulled in two directions... Remember, multiple slants that aren't too severe reflect changing moods and/or temporary fatigue, so be careful before you jump to conclusions."

Combine the major clue of multiple slants with the immature letter forms, the arrangement of the 'blocks' of text in an adult-like layout and the pencil rather than pen, and you can be fairly confident in guessing the age of the author (but don't jump to conclusions - it's rude).

9-11 was a panda job.