How to turn off parental permissions for 18+ family member.

My son is 18 going on 19 and he's included in our family sharing. Until he was 18, I had parental controls set up on his phone and every time that he wanted to download an app, his phone would send me a message requesting permission for the app. It worked great. But, once he turned 18, I no longer find that feature necessary. I've completely turned off parental permissions. I removed my account from the App Store and signed him in under his own name. I think I've done everything I need to do, short of removing him entirely from the family sharing, and I'm still receiving requests for app approval. What's wrong? How do I remove this feature?