Certified GKH Gardening Expert
This cactus will reach a mature height of about 10 feet. At this point, it will be a little under halfway to its full, mature height.
However, this tangled mess of a plant will tolerate pruning, as long as the temperatures are not at extremes (The coldest and hottest parts of the year). In fact, you will find that it grows out of control when left unkempt.
Here is an article that will help you to care for the cactus properly: