Firstly, the other comments about his interest being bonding with you. Definitely leverage as much as you can prior to building anything. But I suspect he actually DOES want to play his idea. He thinks you’re a programmer so could help him, so that’s why he’s asking you. IMO that is.
Secondly, I think you be honest with him and say games are hard and not something you specialize in but if he really want to invest some time learning you’ll help him solve problems and you can do it together. Make sure he’s not just your boss tossing ideas/designs that you have to go implement. Start by googling different frameworks and watching/reading tutorials together. Basically show him the process you’d go through if this was your idea to learn game development. Look into unity or godot, vet solutions, play with some demo apps. Watch some of the videos of people building simple games. Building the basic rollaball game will give him an idea if it’s even something he wants to continue with. Also look for assets that complements his game’s style/theme. Asset development is a common road block so if you start with a character rig and an environment that looks something like what he’s after it will give you some momentum on the actual game mechanics/story/etc. I think if you approach it as a team of equals willing to figure this out, you can’t really lose but don’t expect him to have the fortitude to complete it. Put in as much effort as he does.
Yes! Some of my favorite memories with my pops involved him saying "I don't know, let's figure it out".
E.g.:
Me: "dad can we make lava?"
Dad: "I don't know, it has to be really hot"
Me: "We have a torch, thats really hot, will that work?"
Dad: "I don't know, go find a rock I'll get the torch"
20 minutes of heating a rock later
Me: "I don't think this is gonna work, its not even glowing yet"
Dad: "yeah you're probably right. wanna see something cool tho?"
Me: "Yeah"
* Dad puts the rock in the "safety bucket" of water we had there in case somethigng caught on fire. It steams and hisses and the water gets hot *
Me: "COOL!"
Other good memories include failed attempts to fix broken toys, the time we went on a quest but failed to locate the source of a stream, the rainy day we went fishing in a drainage ditch (where there would never be fish), and so on.
Secondly, I think you be honest with him and say games are hard and not something you specialize in but if he really want to invest some time learning you’ll help him solve problems and you can do it together. Make sure he’s not just your boss tossing ideas/designs that you have to go implement. Start by googling different frameworks and watching/reading tutorials together. Basically show him the process you’d go through if this was your idea to learn game development. Look into unity or godot, vet solutions, play with some demo apps. Watch some of the videos of people building simple games. Building the basic rollaball game will give him an idea if it’s even something he wants to continue with. Also look for assets that complements his game’s style/theme. Asset development is a common road block so if you start with a character rig and an environment that looks something like what he’s after it will give you some momentum on the actual game mechanics/story/etc. I think if you approach it as a team of equals willing to figure this out, you can’t really lose but don’t expect him to have the fortitude to complete it. Put in as much effort as he does.