The pre-flowers on a male plant are sometimes tricky but most of the time you will see a ball, well before flowering. It’s not even May and I’ve been able to know because I had two and one looked like this:
Where the other looked like this:
I don’t have a great camera and those are not my plants but they may as well be twins. I felt confident enough to take cuttings from one and toss a whole plant I had topped. I suppose I could have let it go but I didn’t want any possible pollination. Yield and Potency drop like a stone. Not to get too far off topic but every news story about the rise of THC % in Cannibas over the past 30 years never seem to add that a lot of the potency went up simply by weeding out the males. Ok, speech over. Look for the ball sack. That is your giveaway. A female does nothing with that, and doesn’t grow anything that looks like it. You definitely do not have to flower your plants to get gender.