Young man, a king or Russian noble (5)
I believe the answer is:
boyar
'russian noble' is the definition.
'boyar' can be an answer for 'noble' (I've seen this before). I'm unsure of the 'russian' bit.
'young man a king' is the wordplay.
'young man' becomes 'boy' (a boy is a male child).
'king' becomes 'R' (abbreviation for rex, king in Latin).
'boy'+'a'+'r'='BOYAR'
'or' acts as a link.
Can you help me to learn more?
(Other definitions for boyar that I've seen before include "Noble" , "Russian aristocrat" .)