My eight-year-old son and ten-year-old daughter have checked this book out from the library numerous times. The folds are challenging, requiring repeated attempts and a copious supply of paper (for practice), but the completed models are outstandingly realistic and satisfying.
The authors have provided a lengthy discussion of special papers and wet-folding techniques, but every model can be worked in plain-old origami paper. I'd say that if you've memorized the crane, and if you've worked your way through a couple of intermediate-level origami books (e.g., Kasahara, CREATIVE ORIGAMI), then you've got enough origami experience to tackle the folds in this book. All you need is time, patience, fortitude, and a good supply of origami paper for goof-ups.