Susan was invited to stay with Alek, the younger boy.
There were boys older than Alek.
Truscott compares the through training received in the Army with these weapons way before you are ever permitted to shoot it, and then only under the control of a expert shooter, with the situation in states like Arkansas, where it's legal for a 10 year old to possess a assault weapon without any level of training on safety, usage, or supervision.