Juvenile solver is abandoning this (5)
I believe the answer is:
youth
'juvenile' is the definition.
(I know that youth is a type of juvenile)
'solver is abandoning this' is the wordplay.
'solver' becomes 'you' (the person solving the crossword).
'abandoning' indicates named letters should be taken away.
'this' with 'is' taken away is 'th'.
'you'+'th'='YOUTH'
(Other definitions for youth that I've seen before include "Juvenile" , "period before getting old" , "Early days" , "Youngster" , "Young man" .)