We (Wife, 16 yo, 15, yo, 13 yo, 8 yo and me :)) did our 1st rosary as a family yesterday after Mass and lunch. (I am a Catholic revert and my whole family is joining the Church with me!!! They were all raised outside the Catholic Church - not anymore )
I asked our 8 yo to join us and he initially said no. We got a really cool looking rosary made out of wood and each decade has a different color (He loves rainbows). I made copies of a how to pray the rosary handout I was given at my Church (During my CRHP retreat) and each one of them had a copy.
We started with In the name of the Father and my little guy ran to his room and got his rosary to join, lol. In his own way (he is autistic) but pretty consistent he did the entire rosary with us. I lead the prayers into the 1st decade and then each kid lead a decade with their prayers requests. Our 8 yo lead most of the last decade!!! Praise be to God.
I have to say that praying the rosary as a family is a powerful spiritual experience.
We’ll see how it goes when we pray it within the mysteries :).
So my advice would be to let your 8 yo watch the family do it and hopefully he’ll have itchy ears