Initially nervous youngster lays off newer material (5)
I believe the answer is:
nylon
'material' is the definition.
(nylon is a kind of material)
'initially nervous youngster lays off newer' is the wordplay.
'initially' says to take the initial letters.
The initial letters of 'nervous youngster lays off newer' is 'NYLON'.
(Other definitions for nylon that I've seen before include "Fibre of polymeric amides" , "Synthetic material used in textiles" , "Synthetic cloth" , "Polyamide" , "Unaccompanied part song" .)