I didn't read all the posts, so I don't know if it's been recommended, but the Nike Running club app, beginner 5k Program with Coach Bennet is phenomenal. Download the app here: (H
My wife (not a runner) has tried to start running multiple times and has always quit after a bit because it's just not fun. The Nike program has kept it really fun and perfectly matched to her pace and goals. And Coach Bennet (video recorded coach) is super positive and inspirational. And...she has kept running, because she enjoys it.
I think the biggest goal is for him to enjoy it. If he gets even somewhat "fast" that's cool, but not really what running is about. And then you could occasionally check in, maybe do a run together.
Also you could checkout ParkRun (https://www.parkrun.us/) to see if there are any races near you. They are hyper focused on running accessibility and participation over speed and would be an awesome place for him to join and build community. Again, if there is speed there, it'll come. First, it just needs to be fun.