does a plant have to reach a certain height/age before it will flower or can you flower a smaller/younger plant?
It is better to let the plant get to a stage were it has inividual stems coming off main stem or branches but as the other dude said you can do it when you want
you can flower any time you want... just switch to 12/12 make sure the plant is atleast a foot... make sure it has a strong stem... basicly the bigger the plant the bigger the yield i would let it grow up a little good luck