On solid gold's site, their Holistic Blendz is 6% min fat.
http://solidgoldhealth.com/products/...?id=6&code=160
The Hundenflocken isn't much higher at 10%
I've not tried the holistic Blendz, but the hundenflocken has been eaten here, and relatively well accepted. (Their fav is the wee bit).
Innova Senior on the Natura site has 8%
http://www.naturapet.com/display.php...%3D%2733%27%5D
California Natura Lamb and Rice/Chicken and Rice Reduced calorie also 8%
http://www.naturapet.com/display.php...d%3D%275%27%5D
You will need to find something to increase his calorie count on these lower calorie foods without adding fat since he is still a growing boy.