I grow outdoors here in Hawaii, in greenhouses. Plants flower here year round, as soon as they are mature. Unless...
All that's needed to prevent flowering is to flash your plants with some light in the middle of the night – early flowering worries gone, poof! Just one or more low-wattage, full spectrum LED bulbs do the trick, on a timer. The light needs to hit all over the plant, otherwise lower branches that are shaded from the light will go into flower, while the rest of the plant remains in veg. Some well-placed reflective material can help get the job done.
You don't even need a greenhouse to accomplish this. You can use waterproof outdoor hanging lights.