Old scientist not familiar with fashion (6)
I believe the answer is:
newton
'old scientist' is the definition.
'Newton' can be an answer for 'scientist' (Sir Isaac Newton). I am not sure about the 'old' bit.
'not familiar with fashion' is the wordplay.
'not familiar with' becomes 'new to' (I've seen this in another clue).
'fashion' becomes 'n' (I can't explain this - if you can you should believe this answer much more).
'newto'+'n'='NEWTON'
Can you help me to learn more?
(Other definitions for newton that I've seen before include "Thandie - - , actress" , "Formulator of the law of gravitation, d. 1727" , "Supposedly, an apple fell on his head" , "SI unit of force" , "Unit of force - English polymath, d. 1727" .)