Hi. I know you called last week, and I've been attending to other things much of this week, but I did want to try to respond to what my mother said you wanted.
Before I say anythying else, I want to say this about hardware: no matter what you do, someone will tell you it's wrong. So don't fret about that.
I'm told you don't really know what you're doing (this applies to your grandson as well), which means you shouldn't want to do what I did two years ago, which is buy parts and put them together myself. That gives you two other basic options:
There's a store called Micro Center (there's one in Westmont) that I like for hardware, and they do sell some prebuilt boxes off the shelf as well. They also advertise that they have knowledgeable staff who can help you make parts decisions, and they can (for a price, Ugarte; for a price) build a machine from custom parts.
There are basically four (or maybe five – I'll get to that) things that are going to matter when you are looking at hardware from a simplified perspective:
Any piece of software you want to run is going to have requirements for those four things. For example, on the Steam page for Stardew Valley, the section on System Requirements says it needs a 2 GHz processor, 2 GB RAM, 256 MB VRAM with Shader Model 3.0 and DirectX 10, and 500 MB available storage. That's a pretty boring spec list. On the other hand, the brand-new game HUMANKIND specifies a 64-bit processor of at least a 4th gen i5, 8 GB RAM, at least a GTX 770 discrete video card, and 25 GB of storage, with recommended specs of at least a 6th gen i5 and a GTX 1060 video card. My machine has a 9th gen i5, and anything you would buy/build today would be no worse than that, and the GPU I have does exceed that recommended spec (barely, I think; the 1650 and 1660 replaced the 1050 and 1060, and I have a 1650).
Given that you want a good experience, you want to be sure to meet or exceed the Recommended specifications for any software you want to run. This probably has the biggest effect on your choice of video card, especially for gaming.
I didn't bother mentioning the mainboard, because that will take care of itself with the rest of the specs, whether it's prebuilt or custom. There are two manufacturers in the consumer-grade CPU market, Intel's Core i Series and AMD's Ryzen Series. People will argue until the end of time over which is better. I don't think it much matters. Intel's Core i Series come in i3, i5, i7, and i9; I bought the top-end of the i5 class (not the i7 or i9) available at the time, the 9600K. I would always suggest buying the newest gen you can get your hands on in general, but don't feel like you've got to spend twice as much for 11th gen. The sample prebuilt I linked earlier was a 10th gen i7. I wouldn't suggest an i9 to anyone who doesn't know why they would need it.
Here's where for a gaming rig the prebuilt falls flat. It says "Intel UHD Graphics 630"; what that means is it uses the GPU that's on the processor. I did that for about seven months with my machine, but I always planned on upgrading the GPU when I had the funds. This is a place where you want to watch the specs of whatever it is you (or your grandson) want to play, and try to meet or exceed the recommended spec. Like with processors, there are two manufacturers: NVIDIA and AMD. Who makes the actual card doesn't really matter (it's like who makes the mainboard in a bit I skipped); I've got a GPU made by GIGABYTE, but the important part is the NVIDIA chipset on it. Much like with CPUs, where you can pay out the nose if you so choose, so with GPUs. GPUs also can be hard to find at the high end, because they are in high demand. Again, try to hit at or just above your recommended spec; if it says it recommends a 1660, don't go out and buy a 3070 … unless you can get a good price, of course.
You don't need 64 GB of RAM. You probably don't even need 32 GB of RAM, though if you see a game that recommends 16, consider 32. We have 64 because we wanted to be able to run multiple high-demand applications simultaneously without taxing the system. The clock speed is probably not hugely important. DDR4 natively runs at 2667 speed I think (it might be 2133). I think I've got 3000, but only because it had lower latency numbers than the 2667 I looked at. The sample prebuilt has 3200. Again, I don't think it will matter for what you want to do.
A solid state drive (SSD) runs much faster because it has much lower access times than a traditional hard disk drive (HDD). Our system has one of each, a 1 TB SSD (a nice one, if I do say so myself) that runs the system and a 6 TB HDD for mass storage. I would certainly say for your purposes you want sufficient SSD space to load and run everything, because reducing load times in gaming really does matter. The prebuilt example also has a 1 TB SSD; that's not something I'd skimp on.
So I haven't mentioned anything about peripherals or network connectivity or Bluetooth or any of that, and what matters for you there is going to depend on usage and environment. If the unit is going to be somewhere near a wired network port, wireless networking is less important. (WiFi and BT were an add-on for the mainboard I bought; I did get the add-on card.)
What might be a big deal here is a display, because frame rate can matter, depending on the game. Frame rate is a measure of how often the screen redraws itself. For most of the 20th Century, 24Hz was the common frame rate for films; you saw 24 frames per second when you watched the screen. For my machine, I have connected two Vizio V-Series 40-inch television screens, which have a resolution of 3840×2160 at 30Hz, so I only see 30 frames per second. That's not a big deal for me. The video card would support up to 60 Hz at that resolution, but the screens won't.
So here's the point where the display may matter. If you are looking for a box to play action-oriented games (first-person shooters and the like), a higher framerate is going to be better. You need to make sure that the display will interface with the video card, and whatever framerate you want is supported by both (at whatever resolution). For me, it's more important to have a lot of screen real estate (which is why I have two screens at 3840×2160), but it may be more important for you to have, say 120Hz at a smaller resolution (like 1920×1080). That's something I really don't have any experience with.
I hope that was informative. I'm not a subject matter expert by any means (and there are people at Micro Center who know more about any of this than I do), but my mother said you needed some baseline, so I thought this might help.
Jason