If he wants to play bass, let him play bass. Electric/acoustic guitars don't need to be a step between him and what he wants. If he wants to play an electric guitar, let him play that. Same deal with an acoustic guitar.
I like to think of it this way: If you wanted to go live in a ranch house, or a flat, and you currently lived in a 2-story house, would you buy a trailer in between?
All I ever recommend to my students (and I stand firm on this) is that they still study aural and written theory along with the instrument. Just a little bit of knowledge in those fields and some ear training can immediately set them worlds apart from half of the guitar/bass/piano players/vocalists out there.
You really don't realize just how much difference there is until you see the rehearsals they have (people who know theory vs. people who don't). With a basic understanding of harmony and a decent ear, a guitar player can learn a 2-hour set in a 3-hour rehearsal for the next day. And because of the understanding of theory, it doesn't even require much memorization, because theory leads to chord progression making so much more sense. To the point where the guitar player can just predict what's coming next.
Okay. Sorry for the rant, but that's my honest opinion. Let him play what he wants to play, but push him (don't force him, though) to get some theory behind it. It'll get you more gigs than all your talent put together. I guarantee it.
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I love science, and it pains me to think that so many are terrified of the subject or feel that choosing it means you cannot also choose compassion, or the arts, or be awed by nature. Science is not meant to cure us of mystery, but to reinvent and reinvigorate it. -R. Sapolsky
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