Mine got into trouble at school around that age, for pointing out that his teacher had written a semi-colon incorrectly on the board. She'd put the comma bit at the top and he told her it should be the other way around. She argued with him for a few minutes until the TA confirmed that he was right. <proud but narked>
DS (6.5) asked me, 'When exactly should you use a semi-colon, because I see them all the time?'
Dismissing the idea that he sounded like the little boy in The Sixth Sense (I see semi-colons... all the time.') I gave a vague explanation and then furtively googled semi-colon usage. The next day I carefully explained it to him, whereupon he said, 'I know - I asked my teacher.'
Does he have the makings of a good pedant, do you think? Oh, I would be so proud! Imagine the Georgian family annual newsletter: which we don't do This year, Mini Georgian mastered the art of the semi-colon; we have had a high old time finding him examples to correct!