Young mum, irate, needing refreshment (8)
I believe the answer is:
immature
'young' is the definition.
(synonyms)
'mum irate needing refreshment' is the wordplay.
'needing refreshment' indicates anagramming the letters (the order is refreshed or changed).
'mum'+'irate'='mumirate'
'mumirate' with letters rearranged gives 'IMMATURE'.
(Other definitions for immature that I've seen before include "Not yet adult or fully grown" , "Undeveloped - unripe" , "Lacking in development" , "behaviour of child" , "Not yet adult or fully developed" .)