Youth these days wants johnnies regularly (6)
I believe the answer is:
adonis
'youth' is the definition.
(I have seen 'Handsome youth' mean 'adonis' so perhaps 'youth' could also mean 'adonis')
'these days wants johnnies regularly' is the wordplay.
'these days' becomes 'AD' (as in Anno Domini, after Christ).
'wants' is a charade indicator (letters next to each other).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'johnnies' are 'onis'.
'ad'+'onis'='ADONIS'
(Other definitions for adonis that I've seen before include "Extremely attractive young man from Greek mythology" , "handsome lad" , "Handsome youth - boy from Greek mythology" , "extremely handsome chap" , "ideal man" .)