In all frank honesty, as much as I wanna say "Yup. Exactly why the ratings systems are in place", first game I played was Doom II, age of Ten (Well, technically, I'd say Space Invaders, age 9, but shh), and I've not had any big issues, but the tech has moved on a Lot since those days, so in a way, the ratings rant is still appropriate, but the biggest thing is that games these days Need to be treated with a serious respect, kids, Adults and Parents all.
And TBH, as someone mentioned earlier in the thread, there are Far too many variables involved in the study for it to be considered reliable... Just like 95% of the others that've been commissioned to spook people off buying videogames.