The boss may be a mere boy (6)
I believe the answer is:
master
This could be a double definition.
'the boss' is the first definition.
(I've seen this before)
'a mere boy' is the second definition.
'master' can be an answer for 'boy' (thesaurus). I am not sure about the 'a mere' bit.
'may be' acts as a link.
Can you help me to learn more?
(Other definitions for master that I've seen before include "Virtuoso" , "with 1a [NEW] Jacky may have in nursery" , "Main; overcome; original recording" , "Schoolteacher" , "Lord of a stream" .)