I haven't seen this theory presented anywhere and it certainly isn't anything Bryke have mentioned, but it makes sense to me.
The Air Nomads are patterned after Tibetan Buddhists. In Tibet before the Chinese took over, the monastaries were the centers of education. If a Tibetan child wanted an education he (or rarely, she) went to monastary to be taught by monks or nuns. When their education was complete, the majority would leave to lead more prosaic Tibetan lives; only about 5% would stay at the monastary to follow the more austere clergical (and celibate) path and educate the following generation.
I can see the Air Nomads following the same pattern, children leaving their parents about age five or six and going to the temple appropriate for their sex until their education was done, as early as twelve if -- as I imagine -- only a grade school equivalent is needed for the simple life of a nomad. The majority of the children then rejoin their parents nomadic group while a handful follow the calling to become a monk or nun themselves. The main population may visit the temples from time to time, perhaps gathering on feast days, but most of the time te temples are populated only by the temple staff and their charges.
This would explain why the Nomads are all well-centered, even if they are not clergy. You can imagine the difference between being educated by Monk Gyatso or Sister Iio as opposed to someone like Ms. Kwan that the poor Fire Nation students get. If this speculation is correct, you could have hundreds of thousands of Air Nomads actually being nomads rather than living in one of four fixed places. DesertDog (talk) 16:17, March 4, 2011 (UTC)