i dont think making it 18+ will kill the sport, would p!ss off a whole load of people though. kids dont realy have the spending power to noticably effect the industy, so i dont think their would be any problems there, as for getting new players, you have to be 17+ to drive, but do you see a lack of younger drivers? no, they look falward to it, they get exited about it, then once they can drive, they will. is paintball went 18+ i think it would have a similar effect.
having said that, having no kids playing would lower the standard of play, it is much easyer to pick something up at a younger age, im sure no one will argue against that, so by starting young, its possible they could be "pro" by the time their 18, thus giving a higer number of quality of players, which makes for better tornys.
however i dont see any reason for brining in such a rule, its perfectly safe for kids and as far as behavior gose, simply kick out the problem ones, and leave everyone else to it