Parental Control

[Efficient_Good_5784]

You could also create a new library and move the rest of the movies that aren't age appropriate for him there. You can restrict which libraries are available for each user too.

Then move them back into a single library later when the time comes.

Your original issue with permissions sounds like a bug. I would open a Github issue and see how the devs respond: https://github.com/jellyfin/jellyfin/issues