there is a valid point that this hadeeth regarding ayesha's age is narrated from a sahaba and not narrated from ayesha herself or the prophet, so even though its in bukhari, it only means the chain is authenticly linked back to urwah. Its doesnt prove that urwah was correct in his oppinion. Another question to the OP, can you give any examples in bukhari or muslim where things are authentically narrated by sahaba's but the sahaba were incorrect in their statement. For example, erroneous fiqh rulings (I believe some of the sahaba held mutah and music and other things to be halal for example, can this be traced back to bukhari or muslim?)