Leatherstock, barrel length won't make much (or any) difference on the effectiveness of the shotgun. In the old days you needed the extra long barrels to burn all the powder, not so anymore. Modern ammo has reached it's peak at 22". Most of us old guys shoot long barrels out of habit and the fact that they are a little more user friendly (better follow through). Get him the youth model to start with, it's inexpensive and easy to change the stock and forarm later.
A side note, I spent a BUNCH of money trying to find a shotgun for my wife, (she's a little gal), I finally got her a youth model Pardner 28ga, she loves it, you couldn't talk her out of that gun. Wish I'd have thought about that first...
>>>===> Dave