  We worked our way through age-appropriate Duplos and toddler legos until this year, when we began to faze in the Real Legos among Aidan's toys.
We waited longer than we needed to because our Ella was so very oral that we were certain she'd eat the little bricks. But in March we bought Aidan his first set of Real Legos, it was a small tractor, for the NM trip, and this trip we bought him a much larger, more complicated set (it makes any number of insects).
He's tearing through it! The only downside--and I'm not sure it's such a downside--is that from the moment he first set hands on these Big Boy Lego sets, he lost his unquenchable thirst for floor puzzles. These larger Lego sets are like three-dimensional puzzles in a way, so I can understand how a boring old cardboard puzzle pails in comparison. John attributes much of his engineering-oriented brain to his childhood devotion to Legos. He's more than a little proud of the way Aidan's already doing the 5+ and 6+ level sets.
I bet they curve the age levels a bit to keep kids interested, but I don't say that to John because why burst his bubble? Now we have to find space in the attic for all these giant floor puzzles until Ella is old enough to take them on! She's still taken with toddler Legos for now. 
