Board Thread:General Discussion/@comment-11398218-20140521105018/@comment-8986886-20150610025136

It would seem as though Souls with strong spiritual pressure, such as Captain level Shinigami, age slower than other Souls. If you watch  Turn Back the Pendulum , which takes place 110 years in the past, you'll see that the characters don't appear to have aged more than around 10 years since then. Take Byakuya, and Gin, as examples. They both appeared to be around 15 in the flashback, and around 25 in  Fake Karakura Town .