Gary, you say it is amazing to think it has gone from almost zero to this in a century. I reckon you could have counted the number of commercial planes in the air at any time in the 50s on a couple of hands, and that is a long way short of a century.
It only really started to take off (no pun intended) AFTER the fuel crisis in the 80s, when inflation was rampant, and the cost of flying became affordable.
Last century internal flights in China were limited, then around 2002 it started to change, look at it now, but it is still just the first 300km from the coast.
Compare the flight density between Australia, and Europe. They will need indicators and traffic lights in Europe soon.