Start with a nylon-string classical. First off, it's better for toughening the fingers - you get used to having to hold strings down (there's some feedback from the strings which you don't get from ultra-light electric strings), but the strings are physically larger so he won't cheesewire his fingers to death (as he would with a steel-string acoustic). It also gets you better technique than you'd ever get from an electric - electric guitar teaches you shortcuts which don't make you a good guitarist. Learning these shortcuts is fine, but learn them *after* you know how to do it properly...

Beware of starting him on an Art and Lutherie, or a Seagull, or a Martin, or anything expensive. A cheap classical which plays OK (maybe second-hand) should come in at about $100, if UK prices are anything to go by. (Get someone who plays guitar to check it out first though.) If he sticks it out for 6 months, the reward can be a Squier Strat plus amp. But don't buy anything over $100 to start with.

One thing to check - how big are his hands? If he's big for 14, then a full-size is probably fine. Otherwise if his hands are fairly small then a 3/4 size might be better, and for that it's a 3/4 classical all the way.

Graham.