Strange youth? Very likely (4-2)
I believe the answer is:
odds-on
'likely' is the definition.
(I've seen this before)
'strange youth?' is the wordplay.
'strange' becomes 'odd' (I've seen this before).
'youth?' becomes 'son' (male child).
'odd'+'son'='ODDS-ON'
'very' acts as a link.
(Other definitions for odds-on that I've seen before include "With success more likely as bookie would calculate" , "With success more likely than favour in bookie's phrase" , "High probability" , "Rated likely to win" , "Better than evens" .)