How old does a plant need to be before you can tell its sex? I'm growing outdoors with some random seeds I acquired. Good sun pretty little plants that I'm LST-ing. about 4 1/2 weeks old. I'm wicked anxious.
with outdoors, you are not really in control unless you want to cover them up every night to create an extended dark cycle.
I would find my plants not pre-flowering until the nearly end of July....so would accelerate by moving them into a dark room.
I found that even at 14/10 they would start to flower, so they don't really need 12/12 to trigger
So to answer your question: it's not the age of the plant but the amount of daylight hours that tells the plant it's time to flower
where do you live..... big difference between Florida and Alaska in terms of daylight/dark hours
I now use auto-fem's....no worries about the hours of daylight