Hey, Paul... good to hear your son wants to learn guitar. There are many opinions on what to buy when starting up. I think what Scott said, and the forum link he provided is very useful for that which your son aspires to.
I don't know anything specifically about the Ibanez RGT42DXFX but I do know many yutes out there find electric to be "cooler" than acoustic. But being electric the instrument needs an amp, then there's the world of pedals to add to the mix and so on. Acoustic is nice in that the player can pick it up anytime to hammer out some licks without the fuss of plugging in and setting up.
A good acoustic will run $400 easily. And I stress buying a good guitar (electric or acoustic) because a decent guitar will play well, sound good and inspire more. I've seen many a beginner start out on a cheap guitar only to find the action is too high, the intonation is out, it won't stay in tune and an array of other frustrations. Quality is important for new and seasoned players alike.
I hope this helps... it's just some ramblings I offer in the best interest for your son. I just bought a Yamaha A3M (acoustic/electric) with amazing electronics (pickup) for $750 that rivals a $3000 Taylor imho. Which leads me to suggest an acoustic/electric for the best of both worlds. Food for thought perhaps.
