Informed, foremost of teachers getting on in years (4)
I believe the answer is:
told
'informed' is the definition.
(telling is a kind of informing)
'foremost of teachers getting on in years' is the wordplay.
'foremost of' indicates taking the first letters.
'getting on in years' becomes 'old' (getting older).
The initial letter of 'teachers' is 't'.
't'+'old'='TOLD'
(Other definitions for told that I've seen before include "instructed" , "Related (a story)" , "Authorised - broadcast" , "Produced effect; related" , "Said" .)