If you want to guide him into a career of computer programming with forward-looking skills, javascript would be the logical next step, not python (or perl or Rust or anything like that). Javascript has canvases and SVG and WebGL and anything he creates, he can show it to his friends on a wide variety of devices without them installing anything. Showing off creations can be a strong motivator. It's also getting to the point where you can use ES6 directly in modules loaded into the page without needing all the webpack hassle and still be compatible with most devices.

I'm not really recommending this for a 9 year old, but since we're on the topic of graphics in Perl, I'll go ahead and promote my OpenGL::Sandbox module, combined with the fact that it can run shader demos from www.ShaderToy.com. (but of course, so can javascript) Teaching a kid to think in terms of transformed coordinate spaces will go a LONG way in geometry and trigonometry later in high school and college. I'm doubting a 9 year old can grasp that yet, but who knows, everyone has different strengths. And sometimes early exposure can lead to later understanding.

Edit: Also, there is CmdlineGL if you want to teach him how to do 3D graphics in bash.