Although, if he's the type that'll stare at a campfire for hours on end, zoning out and watching that printer make his first benchy boat might be AOK with him. Otherwise, there's a definite lack of immediate gratification for a younger child too. STL file, putting it into the slicer, choosing your options there, then generating the gcode, and putting the gcode on a SD card to the printer, or sending it over the home network, if the printer is so equipped. Or, if he's the 'obsessively mods Minecraft'-type, all the steps for 3D printing and setup/installing the software on a PC, the settings and adjustments, might appeal to him. Although this has a bunch more potential to become a dust gathering thing taking up space too. And there is tons of things to print in support of other hobbies and crafts. Decent usable ones are surprisingly cheap. There's tons of age-level & skill-level appropriate kits for different things.

And obviously, sit down and do it with him.

A drone, RC car, or some sort of robot, science/engineering/STEM kit that requires assembly and DIY.

3d printed slot car bodies