Our DS4 liked puzzles starting at around age 2. To this day, though, he still doesn't do them edge first. In fact, I have the hardest time getting him to pay attention even to the picture. He seems to look only at the shape of the pieces and then find the ones that fit together. To be honest, I have no idea how he manages to do this. What is clear, though, is that A) he likes them and B) he likes to do them his own way. Early on you can help by surreptitiously putting some relevant pictures nearby so that things work out.
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