Mary - one of the nice things about the guitar is that you can work with 'single note' melody lines and chordal work. I suggest your son try both and see how he progresses; I was a wannabe rock god at the age of 13 and worked hard on lead lines on my electric, but then I grew up, realised I'd look like an idiot in spandex trousers, and took up the acoustic. Since most of my playing is accompanying songs or in sessions (and in both cases the melody is being carried elsewhere) I tend to do more work with chords these days, but both styles are worth studying.