Depends how adventurous the 90 pounder is and how well they pay attention to instruction. The guides arr very good and make it fun. The lower may bore the lightweight ;-)
My 11yo nephew is about 90lbs and had a blast doing the upper. He has no trouble with the rougher spots.
I would do lower.
I would do the upper if you want rapids.
The guide will recommend you depending on other people in your group.
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