Soldier rules - odd characters are youngsters (5)
I believe the answer is:
girls
'soldier rules odd characters are youngsters' is the definition.
I can't judge whether this defines the answer.
'soldier rules odd' is the wordplay.
'soldier' becomes 'GI' (GI can mean a US soldier).
'odd' means one should take alternating letters.
The alternate letters of 'rules' are 'rls'.
'gi'+'rls'='GIRLS'
Can you help me to learn more?
(Other definitions for girls that I've seen before include "Young females" , "Youthful females" , "Young ladies" , "Members of brownies or guides - one of the 14 films" , "Female children" .)