If you’re going to directly connect them using just a single cable then it needs to be a crossover cable and he’ll need to set the IP manually on each end. Most people don’t have a crossover cable lying around. It would be easier to plug both computers into a router/switch and do a network transfer or just get a USB adapter for whatever kind of drive is in the old computer.
Edit: it’s been a while since I needed to dot do that and apparently modern Ethernet doesn’t need specialized cables anymore. TIL.
Oddly, Gentoo was where I started out when I got serious about using Linux. That was when I was in my 20’s and I wanted to get every last bit of performance out of my computer. Also, breaking stuff was fun and gave me a chance to figure new stuff out.
Now I just want stuff to work and be relatively up to date. So I use Debian testing.