My daughter and son were a little younger than that when they wanted to learn ~ does he have a favorite stuffed animal that meeds mending? He'll learn how to sew w/needle & thread, and fix a treasure at the same time!
Then, for a "2nd project" I had my kids use my scraps to sew together a "quilt" for that favorite stuffie... it was a win-win! :) Go for it! My youngest son is now 11, and he designed his first real quilt for his bed at age 7 ~ 300,000 embroidery stitches, all Pokemon. He won't let anyone touch it, and I have to wait until he's at school to steal it for laundering :)