There is a publication, "Insight on the Scriptures", volumes 1 & 2, published by the Watchtower Bible and Tract Society, that can give you an excellent a biography of every person mentioned in...
Their exact age is not known, but "Zacharias said unto the angel, Whereby shall I know this? for I am an old man, and my wife well stricken in years." (Luke 1:18)
There is no clear answer, some youngins are old and some oldins are young. Another opinion: At least 80. On the lighter side. This answer was kindly dedicated to Lazarus