Aptitude shown just around fifty (5)
I believe the answer is:
flair
'aptitude' is the definition.
(flair is a kind of aptitude)
'just around fifty' is the wordplay.
'just' becomes 'fair' (just can mean fair in the sense of showing justice).
'around' is an insertion indicator.
'fifty' becomes 'l' (Roman numeral).
'fair' enclosing 'l' is 'FLAIR'.
'shown' acts as a link.
(Other definitions for flair that I've seen before include "Natural ability/talent" , "Elan; panache" , "Stylish talent" , "Style, panache" , "?lan, dash" .)