You should ask the Neonatologist taking care of your son to sit down with you in family meeting to explain "premature lung" and all the other issues your son is dealing with.
Most likely, "premature lung" means that your son's lungs are still not producing enough of a substance called "surfactant". Surfactant production in the lungs greatly increases in the last month of a normal length pregnancy, so premature infants may not produce enough of it initially. Surfactant helps the little air sacs in the lungs (called "alveoli") to stay open and not collapse.
After birth, even in a premature infant, the lungs are stimulated to start producing more surfactant. Depending upon the baby, the surfactant production increases enough that the baby's lung function usually starts to improve by 2 - 3 days of life.
If your baby required assistance with a ventilator, it is likely that he received surfactant as a medication delivered directly to the lungs through the breathing tube (endotracheal tube). Surfactant is one of the medications that has allowed Neonatologist to take better care of premature infants.
I realized that I didn't answer the last part of your question. Surfactant deficiency usually resolves and does not affect the lungs later in life. Depending upon how sick your son was, however, his lungs may have been affected by inflammation resulting from other factors affecting premature infants. Depending upon the child, inflammatory injury can heal with no long term effects, or it may predispose the child to wheezing (asthma-like symptoms) and sensitivity to colds and other viral illnesses.