veg as long as you can. if you cant wait, flower it now, but every inch in veg now, is 2 inches of space for buds to grow later.
can you flower them now? yea sure, ive seen 6in plants put into flower, and the dude took about 4grams off of it and was happy. personally, i want 4ft plants---> 8ft after flowering, and more than 4grams.