This Japanese finds his age is variable (6)
I believe the answer is:
geisha
'this japanese' is the definition.
(geisha is a kind of japanese)
'his age is variable' is the wordplay.
'is variable' indicates anagramming the letters.
'his'+'age'='hisage'
'hisage' anagrammed gives 'GEISHA'.
'finds' is the link.
(Other definitions for geisha that I've seen before include "Japanese girl trained to entertain men" , "Japanese paid companion" , "He's a GI (anag.)" , "Trained Japanese hostess - his age (anag)" , "Entertaining girl" .)