Your plants look healthy enough, but I have to say they don' t show any signs of being out of the vegetative state. There should be asymmetrical growth, for one, which is your first indication that the plant is ready for flowering. Also, the appearance of your plants should have changed dramatically - being the limbs should have turned upward, presenting the flower to full light. You should also be seeing pistils concentrated in the center of the flower. I see none of this happening and I would have to say that given the size of these babies, they aren't even ready to flower.
That said, if you think they should be flowering, then
check your timer for 12/12 photo period. Also, make sure you're using the correct PH for the strain (some kind of Indica, I would imagine, guessing by the large leaf width on the fan leaves). Also, check N-P-K values. During flowering you do not want to be feeding nitrogen, but phospherous and potassium. (I use a 0-5-4 for my white widow, keeping PH at 5.5 to 6.5 max.)
I'll post some pics of my grow - I'm in the third week of flowering - check them out and see the difference!