I've got a RPI with RetroPi, it... sorta works, but the cheap controllers aren't very good, and there's a noticeable input lag in games like Mario Bros. N64 games don't get a decent framerate. Mind you this is with an RPI 2 or 3 so not the best hardware either.
I got a refurbished N64 as well, works as intended.
"Very old" means different things to different people. If you want to run the sorts of games that used to run on "keyboard plugged into the TV" computers, think Z80, not VR4300.
I got a refurbished N64 as well, works as intended.