I'm not familiar with that particular gun, but my very first thought is to follow the mfgr. recommendations - at least until you can find out a whole lot more about it (and I suspect you'll find it here).
That's great what that fellow did for your son - and for all of us. There's nothing like that attitude of helping someone else (especially a youngster) to get involved in the shooting sports to make a lifelong impression. That kind of stuff is contagious, too.
Have fun, and feel free to ask lots of questions.

IM jaybe