He is telling you it won't hit max draw weight, or you can't bottom out the limbs?

It is common for some bows not to hit the max advertised draw weight when changing the draw length. It depends on the design. You should be able to bottom out the limbs though without damaging the bow. And with a few tweaks you should be able to hit max draw weight as well. If something like this would cause the limbs to crack I wouldn't get that bow because it is a POS bow. Or the kid doesn't know what he talking about.

Then again they don't call them Pull Shoot Explode for nothing

Paul