Wrongly think it's about middle age for a horseman (6)
I believe the answer is:
knight
'a horseman' is the definition.
(knight on horseback)
'wrongly think it's about middle age' is the wordplay.
'wrongly' indicates an anagram (I've seen this in other clues).
'it's about' indicates putting letters inside.
'middle' says to take the centre.
The central letter of 'age' is 'g'.
'think' is an anagram of 'kniht'.
'kniht' placed around 'g' is 'KNIGHT'.
'for' is the link.
(Other definitions for knight that I've seen before include "Honour" , "In Britain, a person honoured by the sovereign for personal merit" , "Honorary title" , "soldier" , "Dubbed chessman?" .)