Board Thread:General Discussion/@comment-4620155-20130410100635/@comment-5551986-20130424101717

Andym221 wrote: how would you explain Isshin, he aged quickly over 20 years?

If you read chapter 535, he was more or less, made completely human. So he will age, like a normal human. He lost his shinigami powers and was put into a human Gigai, I dare say the only reason why Shinji's gang and Urahara and friends, stayed young was because they all kept their shinigami powers.