Explain it like I'm 5! Seriously I've read people have extended the life of computers by installing Linux. What is it about Linux that makes it run better on older computers than Windows? How to swap from Windows to Linux on an old PC? What are the benefits? Who does it suit most? Everyone?
It does extend the life of a computer. It works by putting much less demand on the hardware in order to run (it is not always trying to send data back to some server somewhere either). That being said, if you are using a computer to do image editing or video editing, it will also tank on the Linux machine, just not as soon as if you were running Windows with the same hardware.
Who does it suit? There are so many different flavours of Linux you can find one for any level of Linux user. For first time users, I would recommend Mint (Debian). Ubuntu has been caught skimming user data in the past. You may or may not need to install Ubuntu first to get past the BIOS security on your PC, then wipe that and install Mint (Debian). Although you might not need to do this now. You can find guides on Youtube that will explain how to get past the BIOS security.
My partner brought her old laptops home from work and there's 5 to 8 year old laptops that I'm wondering if Linux on them might make them OK for my 9 year old son to use. He's likely to just use for games and YouTube. Would Linux be a good idea? Are there any games for Linux? Will the old laptop run at an OK speed? I don't suppose there's minecraft for Linux too?
In general, Linux is not nearly as "friendly" to use as Mac OS or even Windows. There exist a lot of "similar" apps to what you can find on WIndows and MAc, but they tend to be slightly "clunky" to use. For example, GIMP and Inkscape are free versions of Photoshop and Illustrator (sort of), but they can be really hard to use if you are just starting out or coming from Adobe. However, if all you want to do is surf the web and get your email and listen to Spotify, then Linux should be perfect for you. So, in short, there is a learning curve. How quickly could your son pick it up? At his age it might not take much time for him to become fluent (I started on DOS, and look how well I turned out
)
Linux games do exist, but there are not as many as your would find for Windows. Minecraft does exist for Linux (Debian and Arch).
Finally how easy is it to install Linux on an old Windows laptop? I'm not into the nitty gritty of IT. I can pick up programs like the various office ones quote easily but not into the techy stuff that much.
It depends on what flavour you choose. If you pick Ubuntu or Mint, it should be a rather painless install.
Libre Office (which is an MS Office clone) works perfectly and can open and save .docx, .xslx files with ease. It is also one of the only apps that can let you open a file format across Windows, Mac and PC without exploding the file. Usually, LibreOffice is installed by default, as is FireFox as the browser.
I will say that just about everything in Linux looks like a 10 year old version of the program compared to what you see in Windows / Mac, for instance MS Office went over to the "Ribbon" interface, where LibreOffice kept the forest of icons. I prefer the forest of icons rather than nested menus that make no sense (like you find in MS Office now).
My advice to you: take the plunge, download the .iso of Ubuntu and install it no one of the PCs. See if you / your son can live with it, and go from there. You will learn more as you go and can venture into different flavours as you go. This is what I did, and now I prefer to run Linux rather than Mac or Windows.