Females tend to be agressive towards each other and are generally larger and more rotund then males.
Toepads can be seasonal in males, but when they are in breeding condition they will be larger in the front and heart shaped. Don't expect to hear the calls they tend to be very quite.
If you see one frog chasing another and setting on them, they are probably both female. They don't need to be sexually mature to do that. If one is "chasing" the other and placing a foot or attempting to stroke the leaders back. Chances are the leader is a male and the follower a female.