You can start LST when they are seedlings , you just have to watch how you do it . Essentially your going to start LST as young as you can in your plants cycle to expose more nodes to the light it wil also help maintain a nice even canopy for your plant , as for the leaves I wouldnt take them off just yet , I would wait till they yellow up and start to shrivel . I say this because your plants are still small and to start to defoliate the plant now will cause it piles of stress that isnt needed that may end up slowing down the growth of the plant . Over all your plant looks fairly healthy I wouldnt change very much , you can start LST anytime now and this like I said will benefit you opening up more nodes to the light helping make your canopy much more even . I hope this information helps you on your quest to become a grow master ! -Happy Growing!