I like the previous post.
I would find out what songs he likes. Then I would use the Learn and Master course; (its not an older persons course). I would also use Hal Leonard method books 1, 2and 3 and Mel Bay method books 1, 2, 3, and 4. (expanded edition) I would “cherry pick“ those courses for the best lesson material.I would also insert songs he likes in place of some of the “open domain songs” those songs kids wouldn’t like.I would also pick up Alfred's "Teach Yourself To Read Music" only because it does seems to show how to “count notations“ better than most. A topic confusing for beginners. I like the Mel Bay books because they have the teacher acc. with lessons and duets. They also have a lot of melody practice.The Hal Leonard books contain a few more contemporary songs. There are numerous beginner song books like the one mentioned in the previous post that could be used. Then there is also Steve’s song hits.There are also numerous beginner classical and fingerstyle books you could draw from to have more material on those methods of playing.
I would do this because Ithink that when you give a kid a electric guitar and then sit down and play “Jingle Bells“ well, I think BB King would say “the thrill is gone”.
Perhaps you already have these books in your “piles and piles”.This would require some extra work for you.
I was just looking at the song "Wild Thing" and it would be easy to insert songs like that into a lesson plan. (With simple open chords).You could also teach a lot about music and theory from songs with complete sheet music. Did he like that song in the Truefire's beginners course? I think they called it "Crazy Thing" avoiding copy right issues I assume. (Which I think is the biggest problem with most lessons, not owning song rights.)Take a look at a couple of youtube lessons and sheet music that's available for hundreds of songs like "Wild Thing".
https://www.musicnotes.com/sheetmusic/mtd.asp?ppn=MN0064772
https://www.musicnotes.com/sheetmusic/mtd.asp?ppn=MN0136542