as someone rasised Catholic, who received my First Holy Communion at age 8 and the mother of 2 boys raised Lutheren who received their First Communion at ages 8 and 9 respectively, I think he can bite my ass when he says kids that age don't understand.
tell him it doesn't matter what he thinks...that GOd and your son are the only ones who can judge when your son is ready and they decided on their time!!!
