its hard to tell this early, but basically the first sign is going to be the calyxes, which is in the same vicinity as those stipules, which look like little beans kinda. If they look like they're coming directly from the branch, then it's a female. If they look the same, but extended from the branch by a tiny stem, then they're male.
if you really have to know the sex ASAP, then as soon as you see indistinguishable little calyxes, cut a clone or two, and immediately induce flowering via 12/12 photoperiod. the sex should become apparent after a few days or so
+rep if this helps