Handsome youth is following American college fellow (6)
I believe the answer is:
adonis
'handsome youth' is the definition.
(I've seen this before)
'is following american college fellow' is the wordplay.
'following' is a charade indicator (letters next to each other).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'college fellow' becomes 'don' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'don'='adon'
'is' after 'adon' is 'ADONIS'.
Can you help me to learn more?
(Other definitions for adonis that I've seen before include "Extremely attractive young man from Greek mythology" , "beau" , "Beautiful (Greek) man" , "Said no to the Greek youth" , "legendary Greek noted for good looks" .)