The longest any dragon blooded has lived has been the Scarlett Empress, and she's 800. That's about the same time that the great contagion occurred and wiped out 90% of *everything* that lived, dragon-blooded included. Old dragon blooded are around 300-400 years. Most dragon blood die through violence way before then. The number of terrestials that reach old age has been bandied about at 1/3. There's apparently a tremendously high turnover rate.
I was wrong, however. I admit it! (Make note of this. It almost never happens on the internet. You could probably count the times that it's happened on one hand...)
In the interest of accuracy, here's the real answer, and the sources.
Pg. 192 of Sidereals says that there's about 100 million people in each direction. That means that there's an upper-limit of 50k dragon-blooded world wide.
Also, there is this:
MoEP: Dragon-Blooded - page 226
“The 761 Realm census placed the number of Dynastic Dragon-Blooded in the Realm (included lost eggs adopted to Great Houses) near 10,000. This might be as many as half the entire world’s population of Terrestrial Exalted, and the world knows that it’s there.“
So we basically have contradictory numbers. MOEP: Sidereals combined with rough calculation numbers puts the upper limit at 50k, while MOEP: Dragon-blooded places the upper limit at 20k.
Those are the canonical numbers you have to work with, and I would tend to lean towards the 20k, since it is derived most directly and it fits into my view of creation as a greatly diminished world.
This still places the number of Dragon-blooded contained in a single city-state to something less than 7k, since the entire direction should only have around 10k as it's upper most limit. Granted, lookshy does have about 1 terrestrial exalt per 100 people, we're talking of a population that is generously estimated around 120k, that would give you around 1,200 exalts. The numbers I've seen bandied around by developers after doing a quick google search suggest that there's 500-700 exalts in Lookshy, which would place Lookshy's population at around 70,000 or so, which seems right.