Flowering before the plant is sexually mature is stressful to it and you might even get herms.
The plant can get as large as its pot, available light, and vascular system can support. Outdoors, wild sativas can reach over 15 feet! Yow!
Indoors, you want to keep them SHORT because the light can only penetrate a little ways- it's not the sun!
Always give enough light and root space to make your big plants healthy. If yoiu are limited on either, grow more, but smaller, plants.