honestly, i don't even think putting such a law will change much, i mean how are they supposed to know the age of the person playing the game? u may suggest forcing people to put their real information but its too easy to work around this, there is no real way to be able to tell if the player is under the recomended age.

second, how in the acual fuck are they supposed to know which games are more addicting than others? everyone has a different taste and even if the game is addicting it could easily fail if its generic or the developers do a poor job with the updates. and if the game is addictive to kids it may not be addictive to adults which is going to make age restriction nothing more than a retarted idea that'll kill the game instantly. in short, you can't stop addiction from spreading unless you kill the game.
third, concerning adult games with sexual content and alot of gore and violance.well i don't think this is going to affect underaged players in anyway, i mean i used to play +18 games like god of war(it was my favorite acually) and prince of persia...ect at the age of 7 and it didn't affect me in any way neither did it effect other people i know.

the argument of restricting age for games is just retarted in my opinion because the only basis it has is adult assumptions, no research nor my ass.
forth (and last), if a kid is getting addicted to a game that he forget about school and pretty much his future i think the responsability should fall on the parents for letting their child play as much as he want to.