You can put it into flower anytime you want, the plant size will double or triple in size when your flowering, most people flower early to keep the plant small and harvest quicker, but the more you veg the bigger the plant and bigger yield. You could go ahead and put it into 12/12 now if you really wanted to, how big is the plant?
EDIT: You should try and also top your plant, this will make it get even more bushier, I've done it to my girl which is flowering right now, after i topped her she got bushy as
1st pics is just few days after i topped you can see how there wasn't to much leaf production and looked skinny, 2nd pic is like 3 weeks later i think after topping, huge difference