Im not sure if my leopard geckos are male or female and they seem to be staring at eachother strangely.?

I got my 2 leos when they were very young (I'm not positve how old they are now I would guess 12 or 13 weeks ) but I keep checking for the bulges that males have near the vent and I don't see any. I have noticed recently that when they hunt crickets sometimes they get face to face and stare defensively at eachother. I haven't seen them nip eachother but I'm worried that will start happening. How old do they have to be to sex properly? And is this staring just a hunting thing or are they fighting? Just for info if you wondering...I have them in a 30 gal tank set up the right way with reptile carpet a warm side 85-90 degrees with a warm pad and a cool side with hides on both side..a humid hide and water dish. I only feed crickets and they have a small calcium dish also. I don't use a light right now in the summer because it is very warm in there already and they get a lot of natural sunlight.