Welcome.
Ooops...
Ooops...
It's no prob, youngsters do look like either gender.
That explains it...
Just watch for elbow fins and you'll be right as rain. 
So, do females have elbow fins too? Or are they shorter?
Females don't have elbow fins, instead, they have two ribbon like fins on their bellies. You can see them on some of my pictures.
Oh! Thanks, that's easy to remember.
No prob!