My plants are a month old and has tons of veg growth. I can see all the little pre-flowers I think and I was wondering if i should start to flower them so i can make sure of the females. The plants are only 8 - 10 inchs tall
They will stretch during flower, so if yo have proper lighting to deal with an extra 4-8 inches of growth, then i'd wait. Otherwise i'd flower them now
If you can see pre flowers you can sex the plants before flipping the lights. Get a 30x magnifier ($5 for a loupe at Amazon) and take a look at the pre flowers and weed out the males.