They (And by they, I mean some major company that claim "BLAH" is unsuitable so the kids can't see it, forgot the name) want only people 13 and older to join message boards because they think "It'll be unsuitable and have bad words for them lol it's a bad example". But usually, People just lie about there age.
Still, back on topic. I joined when I was 10, I lurked until I was eleven, also known as my noob period, I lurked more until about... some time in '07, because I felt I should leave the board. (I made a really nooby mistake for answering a question in a topic.) 10 year olds have feelings too :(. Now I'm 12, and I probably won't lurk any more, because I feel like I'm accepted member of the board.
So, I didn't lurk just before I joined, I also lurked after I got yelled at by another user.