Asymmetrical and symmetrical branches

Hi. First grow here. I have 5 beautiful plants grown from bag seed this first grow. They are at 6 weeks. I have a ponderance for some more experienced growers out there. Wish I could send pics but camera is out of service right now, will try at a later date. The branches at the top of my plants have already started to grow asymmetrically, an indicater that the plant is entering the flowering stage according to J. Cervantes, in, "Marijuana Horticulture, Indoor/ Outdoor Bible. " I have the plants on an 18/6 light schedule. I don't really understand why they are entering flowering stage already. It will be 2 more weeks before I'm supposed to be able to take clones, my first time by the way, all advice here helpful, well read, but still nervous, lol. Do ya'll think I'll be able to use any of these plants as mothers? Thanks ya'll, this community has been priceless to me, you've all helped me in countless ways already, looking forward to some input.