How do souls age in Soul Society?
People cannot die of old age resulting in the Captain Commander keeping his position for a thousand years.
There are some souls who look like kids and some who are adults. In the manga, the makers flashbacked into the past of the Captian Commander showing that he had black hair instead of looking like what he was then. Also, when Ichigo left the Precipice World he aged what looked like a couple years.
So how do souls age in Bleach?
The only explanation I can find is on bleach.wikia.com, which says:
One never gets hungry (if she or he doesn't have spiritual powers) and aging is slowed to a great extent, with lifespans of 2000 or more years not being unheard of, though such ages are limited to Shinigami or other Soul Society dwellers with high spiritual power.
There is also an explanation on http://tvtropes.org/pmwiki/pmwiki.php/Headscratchers/BleachSoulSociety that essentially says that it is really inconsistent within the show and that there are a number of different theories, including that characters age inversely proportional to the amount of spiritual power that they use and that at some point aging just stops.
To summarize, there doesn't seem to be a clear explanation in-universe, but the aging is slower than usual, with much longer life-spans than regular humans.
Souls without spirit power do not age in soul society. They also don't hunger and there is no evidence they are doing anything but waiting for the allotted time they must spend in Soul Society to pass before they are reborn.
In Chapter 0, the pilot chapter of Bleach that was later reprinted in Book of SOULS, the "magic number" was 80 years. But Kubo has not stated how many years a soul must spend in Soul Society in the proper Bleach storyline.
Anyway, that aside, the point is that Rukia and Renji aged, because they had spiritual power. It was also why they could become hungry and could become Shinigami. "Shinigami" can and do age. They also give birth, die of old age and basically do everything humans do. Except that their lifespan is usually measured in hundreds of years and not decades.
this is years late - but since it was the first google search result for my questions - I figured this answer might help someone else.
If you're not suppost to age in the soul society, how does rukia and renji grow up from kids in "hanging dog"?
Souls without spirit power do not age in soul society. They also don't hunger and there is no evidence they are doing anything but waiting for the allotted time they must spend in Soul Society to pass before they are reborn.
In Chapter 0, the pilot chapter of Bleach that was later reprinted in Book of SOULS, the "magic number" was 80 years. But Kubo has not stated how many years a soul must spend in Soul Society in the proper Bleach storyline.
Anyway, that aside, the point is that Rukia and Renji aged, because they had spiritual power. It was also why they could become hungry and could become Shinigami. "Shinigami" can and do age. They also give birth, die of old age and basically do everything humans do. Except that their lifespan is usually measured in hundreds of years and not decades.
