If it's available to buy for £13 it shouldn't be too bad surely?
Nods slowly at Majestic
You're right dear, anything under £50 on bomb-making et al is absolutely fine.... 
OP IME 13 year old boys are pretty suggestible so unsurprised he bought it after his 'friend' recommended it. I would though be having very serious conversations with him about why he is interested and does he 'get' how [can't find right word] xxxx it is.
Def a vote for sending it back, and a
to those expressing surprise your child has access to.... Amazon. Porn hub, nope; Amazon, pretty normal IME 