A world where, instead of aging in years, the people age in knowledge. So, instead of dying once a general age was reached, they die once they achieve a certain amount of knowledge. A man could live forever if he never learned anything, or could die after reading a few choice books. Of course, the knowledge of the land would be regulated, like medical drugs.
What a narrow street! The bowed windows of the upper floors encroach on the view of the bowed windows opposite, making it all very dark and shady down here in your carriage. You feel it slow down and stop, and there are raised voices outside. Craning your neck out of the door you see a smug cartsman ahead, whose cart is blocking just enough of the narrow street to make your passage impossible. He appears to be waiting for you to move, but your driver is hurling abuse at him and your horses are getting restless...