I have a ~22 inch torso. I bought the osprey poco plus child carrier which says it supports 22 inch torsos. I went a couple three hour hikes this weekend and my shoulders were done at the end of each. this isn’t normal, right? I am thinking of trying another carrier, but i am worried there are no child carriers for tall people.
The Osprey fitting guide for your pack says it can adjust to fit torsos 15-21". Have you extended the back fully, so the shoulder straps are as high above the waist belt as possible? If so and it’s still too small, you may be out of luck.
You might try cinching the waist belt higher up (the buckle covering your belly button, or just below it) and loosen the shoulder straps as mush as you can. The weight in the pack should be supported by the waist belt, not the shoulder straps.