Also, the thing you have circled is indeed the preflower area and where the actual flower/calyx will appear, but the plant is not quite mature enough yet to know its sex. As it grows in veg, you may see either a pair of white hairs spring out from there (different than the 2 green spikes on each side of that node) or it'll start developing 'balls' which are baby pollen sacs. The time it takes for them to appear varies as widely as strains vary (I hate that answer

), but (very generally) start looking around the 6th to 8th nodes and see if you can guess the sex. It could take another couple weeks to a month to see sex if you're not in any hurry or worried about watering/ferting for that time, or it'll show sex pretty quickly when you go into flower mode.
My main reason for ever worrying about sexing is to ID the females and take the clones before switching over, versus cloning from flower which is more stressful to the donor plant.