I would start on acoustic for all the reasons given. It is more flexible, you can build up the hand strength and you can translate the chords, scales etc to an electric later on.
However, if all he really wants to do is sound like the rockers, he may as well start out on electric from day one. You can bend up a whole tone without risking a snapped string and you get round to using more of the fretboard earlier (though not necessarily better). My six year old had a few months of lessons on classical guitar, but now he likes learning Beatles and Stones licks on the electric, because it sounds noisier and more distorted. He is not turning into Eric Clapton, but he is at least picking the thing up and playing it.