I think most of the experts in whatever-field-this-would-be (probably child psychology) would use an age bracket 2-4 years lower. Abstract thought develops parallel to the realisation that the universe is not you-centric. A recent study (in The Lancet maybe - I think we discussed it here somewhere) showed that perception of sarcasm is not complete until well into the teenage years. Concrete versus abstract thought would be tested by use and understanding of sarcasm and metaphor, and the ability to explain proverbs.

That was a whole lot of random information. I can add more (or PM) if anyone wants more info, of which I have quite a bit given that this is my planned specialisation. One day.

And what's with the medical questions today WW?