Shotacon and computer illiterate?

I mean the over-sexualized little boy was super creepy. Is this shotacon (opposite of Lolita with a little boy as a sexual object) even legal?
Also, in an early scene the boy has to explain what "install" means to the 17-year-old girl. I checked the year the movie was released, 2004, any idiot would know how to install stuff on a computer and at least have heard of it. Why was the girl portrayed so immaturely, even the little boy is more mature than her?