Go Used
If he really wants a road bike (I did at 12), don't overlook the used market.
The first step is to confirm the type of bike, and make sure the design matches the intended riding. For example mountain bikes are perfect on local off road trails, but not going very fast or very far. Hybrids work great on rail trails, etc.
When returning to cycling after a few years off I found an older quality Trek road bike built with all Ultegra components, with clipless pedals, shoes (new and my size!) and a helmet for $200, and road it on a 540 mile tour.
If your lucky, you will have a bike dealer in your area that sells quality trade in's. As most bike shops make the majority of their money on repairs, this is an excellent strategy (IMO) that many shops sadly frown upon for some odd reason.
The default answer of course is Craigslist.org, if you are in an area that is actively used.
Take your time and buy what will make him happy, and fit your budget.