The kid's doing great IMO & see no reason for you to denigrate him as "non-financial". Stay out of his way unless asked. Independence is good.
This is what I was thinking. Give him a few suggestions but don't micromanage. It's the problem with our society today that many adults can't function without parents doing things for them. He needs to fail a couple times to learn. My first job I ran up a credit card bill quick which I couldn't afford to pay off at the end of the month... and I then realized I couldn't spend so much. It's a lesson. It's valuable.
To me the whole CD ladder thing sounds way overly complicated which I assume is not a huge sum of money. Sure if he's making $500k a year then do all that but assuming he is making a modest sum I wouldn't get all complicated.
Roth with etfs and forget about it for 40 years.
Also, I send the idea about Millionaire Next Door. Go big and buy a copy for ten bucks. I also like Andrew Tobias' book which covers a wide range of financial topics. That's another ten bucks.