You can however, rather than actively trying to steer him off anything, try to expand his horizons into different types of game, whether they by cutesy or gorey, depending on whatever takes your fancy.
Childishness can be quite useful, particularly in instances when you're a Swedish Ninja named Olga who just rolled a critical fumble and set her own arm on fire (which I did yesterday) - laughing at yourself with your mates is a lot better than being pissy at that 1/20 chance of rolling a 1
Give an F2P a shot, they're obviously free, though downloading might take an age. There's a vast array of Free-to-play MMO's out there, some of them good, some of them an utter waste of time and space.