This guy is a jerk. Parents should be allowed to buy whatever the fuck they want for their kids, at least the mother is involved with what her son buys. Also 14 years old seems like a fine age to be playing Left 4 Dead. I think I was 14 when I first played it.
To me, he seems like a pretty cool guy. Don't see why everyone is blaming him for what has happened; it's quite clear that even if his actions indirectly inspired these attacks, it's more Sony's fault than it is his.