Measure bringing age into focus (10)
I believe the answer is:
centimetre
'measure' is the definition.
(centimetre is a kind of measure)
'age into focus' is the wordplay.
'age' becomes 'time' (I've seen this before).
'into' is an insertion indicator.
'focus' becomes 'centre' ('centre' can be a synonym of 'focus'**).
'time' inserted inside 'centre' is 'CENTIMETRE'.
'bringing' acts as a link.
(Other definitions for centimetre that I've seen before include "From a little distance" , "Short distance" , "Short length" , "About four tenths of an inch" , "not giving an inch then?" .)