Senior citizen courageous, but no leader, endlessly severe (7)
I believe the answer is:
oldster
'senior citizen' is the definition.
(I've seen this before)
'courageous but no leader endlessly severe' is the wordplay.
'courageous' becomes 'bold' ('bold' can be similar in meaning to 'courageous').
'but no leader' means to remove the first letter.
'endlessly' means to remove the last letter.
'severe' becomes 'stern' (I've seen this before).
'bold' with its first letter taken off is 'old'.
'stern' with its final letter removed is 'ster'.
'old'+'ster'='OLDSTER'
(Other definitions for oldster that I've seen before include "Veteran" , "codger" , "A man getting old (colloq.)" , "one getting on" , "Pensioner" .)