Plants too Tall for LST

We don't know anything about your grow so... What are you growing? Photo, auto??? If you are growing photo then you can prune the top of the plant and cut some height. You can also do some training. Since the plants are a bit old you will have to move slowly. Bend a branch a medium amount and wire it in place. Then a day or two later bend it some more. If you are growing auto's then I would not trim. I would just do LST and try to deal with really tall plants. I use light to help control the size of my plants. During veg I will give more or less light to make the plant the height I want. It's not perfect and the strain still has a impact but you do have a fair bit of control. With more intense light the plant will grow shorter and have a smaller distance between nodes. Less light causes it to grow taller and with more space between nodes.