If there's a chance he might get more into it (it can be addictive!), I'd recommend getting one of the light versions of a higher end package so that the skills transfer during any upgrade will be easier - Premiere Elements, Vegas Movie Studio, etc. Be aware that the price of Pro versions of the established video editors range from "expensive" to "are you f-ing kidding me?" though. Well established packages will also have more "how to" tutorials on YouTube, etc., are more likely to be supported by third party FX plugins, and get bugfixes/codec updates earlier, which might be worth keeping in mind if you might be in the frame as the unofficial support guy.
As to which one, most offer "try before you buy" downloads, so grab those and see which UI he prefers; in my experience you'll find that at least one will just feel intuitive right of the bat, which should help narrow down your options. A good selection of wizards and pre-baked effects that can be tuned will also be hugely useful for someone getting started and won't be too sure of how to achieve a given look/effect. Finally, don't underestimate the usefulness of support for multi-CPU and GPU acceleration either and make sure your hardware is fully supported; you'll spend a LOT more time waiting for videos to render without them!