If their kept in a group of say 5young, 3 will be female and 2 male They can change sex though if the group size changes or some are seperated.
if its a group of 3 the 2 female and 1 male.
this is based on research and is not 100% certain.
if you get the group together the males will have the same shape tail from tip to base i.e. even width all the way whereas females it will be thin to thicker then to thin again working from base to tail tip.
when i mean thin its not litterally thin but the females tail width go wider after the base of the tail!
very hard to explain! and very hard to sex when young!