My son who is eleven shoots a Mossberg 500 20GA - with an adjustable LOP. I have made the following modifications to reduce the recoil a lot (less than the 1100 20 GA.) Added a limbsaver recoil pad - $20 at Walmart, put a stock cover on with a padded comb, added a lead bar inside the stock(wrapped in foam). The gun has very little recoil weather he is shooting slugs with the rifled barrel, or using the field barrel and 3" Hevi-shot loads. The combo of weight, the recoil pad, and the padded comb really makes a huge difference. The next step would to get a shoulder pad, but we didn't need to.

Good luck! :-)