Decorator gets keys for youngster (7)
I believe the answer is:
tiddler
'youngster' is the definition.
(synonyms)
'decorator gets keys' is the wordplay.
'decorator' becomes 'tiler' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'gets' means one lot of letters goes inside another (gets can mean captures or absorbs).
'keys' becomes 'dd' (two D's - as in the musical key of D).
'tiler' going around 'dd' is 'TIDDLER'.
'for' is the link.
Can you help me to learn more?
(Other definitions for tiddler that I've seen before include "Small fry" , "Small thing" , "Small fish (or child?)" , "Minnow" , "One small" .)