My teenage son started shooting trap with a cheap Tristar gas-powered semi-auto. Once it became clear that he was going to keep up with the hobby, we upgraded his shotgun because there were some reliability issues with the Tristar and my son loves to shoot doubles when he can. He is very lean and hasn't filled out his frame yet. His first round of trap was always his best score, so fatigue seems to be an issue. For him, I didn't think it was recoil but the weight of the gun. I got him a Benelli Ultralight and now he won't go back to the Tristar. Recoil is a little more stout, so we just lightened up the loads and all is well. For him, it is easier to swing the (really light) Benelli and if you can hit a clay with 1-1/8 oz load you still hit it with a 1-oz load. That, and you can wear a vest with a recoil pad.
Now, he is getting bored with trap, and I think the Ultralight is well suited for Sporting Clays and 5-stand as well.