Have him try on a few. Better if he can try them.
No fit, not hit.
The fit of the shotgun is more important than the brand or model.
If you belong to a Club, go there, to the Trap or Skeet field, and ask for advice. You'll get too many opinions, but shouldering and shooting a few things will help.
You don't give his age, but if he's <18, he'll likely grow, so plan to get a gun that can have the measurements tweaked.
Oh, yeah.....no fit, no hit.
Any of the above suggestions is fine - but don't discount an auto, or break-action that feels "right" if the $ is doable.