How to check if application on Google Play would work on other (not own) phone?
Let him try installing it via Playstore. If it's "incompatible by design" (e.g. requires Android 4.x while he has only 2.3), Playstore would refuse to install it and give the hint "not compatible with your device".

Apart from that (and if the app description doesn't give a clue):


check the comments for hints (take care for their date, compared with the "last updated" timestamp of the app; AppBrain lists the history of an app nicely on its "Changelog" tab)
Install the SDK on your computer, and add the corresponding AVDs to it to test out for yourself
Ask for the specific app on a forum, whether anyone can confirm it's running on Android X.X.X / the specific device / ...
Ask the dev (and if doing so, suggest to include such hints with the desc)