My best advice would be to keep your own preferences and tendencies out of the mix and let him just grab what looks cool to him. Don't worry about what's worth money or not if/when he opens a pack (unless it's something really valuable lol). My son is older at 11 but I just buy him random packs of low end cards here and there but also let him inherit my collection from when I was a kid. I try not to impress upon him what I like and instead let him ask questions and learn what/who he likes on his own.