How about 8yrs old? He knew what he was doing, he planned it.
http://www.nytimes.com/2008/11/11/us/11child.html
You guys are fully comfortable in executing an 8 yr old as well? He killed therefore he should be killed himself...right?
Its easy to say in the sterile world of the internet but in practice, killing a child is MUCH more difficult.
So what age?
If 12 is too young, how about 13? If 13 is too young how about 14? 15? 16? 17? What is it about one particular magic number that after that birthday capital punishment is OK, but before it not?
Or, working backward, at what age does a cold-blooded, consciousless killer get a "bye"?