I'm with bee-dubya and Cluin. Every rocker worth knowing about started on an old acoustic. (except maybe Eric Clapton. BUT he's Eric Clapton and we're not.)

These days its very common to get acoustics with certain electric-guitar features, like a built-in pickup, slide EQ/preamp (set of tone controls), on the side, and cutaway body style (ask at the store). A well-chosen one, properly set up, will be a good acoustic starter guitar, but if he wants to explore his inner rocker, just plug it in and turn it up loud...it won't be like a solid body electric, quite, but it delivers the ROCK OVERDRIVE BODY VIBRATION quite effectively.