Old savant did change first, being underprivileged (13)
I believe the answer is:
disadvantaged
'underprivileged' is the definition.
(similar in meaning)
'old savant did change first' is the wordplay.
'old' becomes 'aged' (similar in meaning).
'change' is an anagram indicator.
'first' is a charade indicator (letters next to each other).
'savant'+'did'='savantdid'
'savantdid' is an anagram of 'disadvant'.
'aged' after 'disadvant' is 'DISADVANTAGED'.
'being' is the link.
(Other definitions for disadvantaged that I've seen before include "Put in an unfavourable position" , "In deprived circumstances" , "Socially or economically deprived" , "In unfavourable circumstances" , "Handicapped" .)