Dissolute youngster mostly covered by spots (6)
I believe the answer is:
rakish
'dissolute' is the definition.
(I've seen this before)
'youngster mostly covered by spots' is the wordplay.
'youngster mostly' becomes 'ki' (I am not sure about this - if you are sure you should believe this answer much more).
'covered by' means one lot of letters goes inside another.
'spots' becomes 'rash' (I've seen this before).
'ki' going within 'rash' is 'RAKISH'.
Can you help me to learn more?
(Other definitions for rakish that I've seen before include "Dapper" , "Marked by unconventionality or disreputableness" , "Disreputably dashing" , "Dashing and slightly disreputable" , "Jaunty and irresponsible" .)