Do you want to hear something totally nutty? Or at least it seems nutty to me, but true?
When DS7 first started playing videogames, my friend's DD (who is 6 mos. older than DS) had also been playing games on the family computer. The DD started throwing temper tantrums when they told her to turn it off, so first they told her she could no longer play; then they let her earn playing time (in 5 minute increments) for good behavior and doing chores. The most they'd let her play in one sitting was half an hour, I think.
So when DS started playing I thought nothing of it, until I noticed he was having fits when we told him to shut it off!
He was very angry, threw the controller, whined about how we NEVER let him do ANYTHING FUN...! WTH???
I told DH about my friend's DD, so we started limiting his playing time. We also told him that he could not play whenever he wanted, he needed to ask, and also that if he throws a fit when we tell him to turn it off, he will NOT PLAY AGAIN for a very long time.
That worked well for awhile. But now that he's older and we don't monitor him as well, he will ask for permission to play while I'm making dinner, for instance, and then I realize he's been playing for too long. I'll tell him to turn it off (as I'm going to do something else) and he'll say, "OK, I'm just going to finish this one thing..." and when I come back around he's onto another thing!
It's always, "Just a minute..." or "OK, I'm shutting it down now" and he doesn't. So gonna have to lower the boom on that too.
