This is my experience too. Provide access to a computer that the student has full control over (to experiment with operating systems) and allow plenty of time to work on programming projects. Even though playing video games can be a waste of time, modding and recreating them is a good programming exercise and should be encouraged. That’s how the few twelve-year-olds I know got into programming, and they now make more “serious” projects of their own.

Edit: and since you’ve got plenty of experience, you can be the perfect first resource for your 12-year-old to ask for help.