Express sorrow about each book finally showing signs of age? (6)
I believe the answer is:
creaky
'showing signs of age?' is the definition.
(I've seen this in another clue)
'express sorrow about each book finally' is the wordplay.
'express sorrow' becomes 'cry' (I've seen this in another clue).
'about' indicates putting letters inside.
'each' becomes 'ea' (abbreviation).
'finally' indicates one should take the final letters.
The last letter of 'book' is 'k'.
'ea'+'k'='eak'
'cry' going around 'eak' is 'CREAKY'.
(Other definitions for creaky that I've seen before include "Could describe a loose floorboard or arthritic limb" , "Like an unoiled hinge; badly performed" , "making grating sound" , "Tending to squeak; badly made (colloq.)" , "Old-fashioned (and unoiled)" .)