Board Thread:Questions and Answers/@comment-6088207-20130124020332/@comment-9330998-20130125092838

Of course, we don't know exact numbers. I've just estimated from their physical appearances, I don't claim it's canon or anything ^^. Remember how old Yamamoto looked ~2,000 years ago, some unknown period of time before establishing the Gotei 13? Unless Unohana ages in reverse, he indeed was noticeably older than her (physically).