The member from Yarmouth is a mere lad (5)
I believe the answer is:
youth
'mere lad' is the definition.
'youth' can be an answer for 'lad' (I've seen this before). I'm not sure about the 'mere' bit.
'the member from yarmouth' is the wordplay.
'the member' becomes 'arm' (member can mean a limb).
'from' indicates named letters should be taken away.
'yarmouth' with 'arm' taken out is 'YOUTH'.
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for youth that I've seen before include "Young man" , "Youngster" , "Youngsters" , "Lad" , "Juvenile" .)