Board Thread:Questions and Answers/@comment-3001900-20131024200959/@comment-2089817-20131026210833

If we take Kubo at his word, the bodies of the Shinigami and subsequently the bodies of spiritual beings are projections made by their soul. In other words, the soul becomes the body. And it is commonly believed in many psychological sciences that the mind can age at various rates, depending upon a person's experiences and emotions; hence why you can have a young man of thirteen being of far more sound mind and maturity than a person in their twenties, probably due to the way they were raised and went through life. Similarly, we can say the soul itself can age at various degrees and rates based upon a person's experiences and the way they have dealt with their experiences. So given that the soul becomes the body, the aging process would undoubtedly reflect this principle when it comes to spiritual beings.