Very old can start to guide election (6)
I believe the answer is:
voting
'election' is the definition.
(thesaurus)
'very old can start to guide' is the wordplay.
'very' becomes 'v' (abbreviation).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'can' becomes 'tin' ('tin' can be a synonym of 'can').
'start to' suggests taking the first letters.
The first letter of 'guide' is 'g'.
'v'+'o'+'tin'+'g'='VOTING'
(Other definitions for voting that I've seen before include "Taking part in election" , "polling process" , "Casting a ballot" , "Selecting by ballot" , "Indicating choice or opinion, in an election or debate" .)