This may be a vauge reply, but I don't think that there can be one set age across the board. What if one child never is told about Christ until the age of ten where as one has been raised in church since birth. Obviously the one raised in church will have some understanding of who Jesus is. In saying that is it right to believe that the ten year old who's never heard of Jesus will be held accountable. I believe that if that ten year old passes away before ever hearing the good news of Jesus Christ he won't be held accountable.