Board Thread:Questions and Answers/@comment-5047068-20170924233337/@comment-27392440-20170929001454

They never reveal why these humans do not seem to age and many other factors about how they work (like how vollstandig is attained or works) but I imagine that since they constantly do things like blut they probably are somewhat altered enough from the human norm over time so rules do not apply to them. Also, people in soul society don't age at a normal pace either so ever since the Quincy hid out in soul society, which would have meant converting their bodies to spirit particles, they may have had the same illogically slow aging rate as a soul (with souls that are stronger and more dynamic seeming to retain their youth until they become more stagnant and set in their ways like Yamamoto was)