Journey is excellent and quite mature. no blood, no gore, no fighting, but mature nonetheless.
If you can kill humans with things other than guns (swords, etc), I'd recommend Dragon Age Origins, Skyrim, and Assassin's creed 2 and its sequels.
If you like RPGs at all, you should pick up Ni no Kuni. Not really mature per se, but a damn excellent game and an example of how jRPGs need to be done (and why Square Enix is full of shit and needs to die in a fire)
unfortunately, most games these days center around killing people with guns. that's just how it is