IMHO, there is no reason a boy can't make a quilt, we have some great quilters here on this board who are men. As for his age, do you have a way of setting the speed on your machine so he can't put his foot down and zoom away?
I started my grands on a hand crank singer. I reasoned that they would at least have one hand out of the way!
You could possibly sit him on your lap and operate the pedal for him, while he guides the fabric through.