In the process of quitting cigarettes. if i can quit now(age 25) will i most likely avoid all tobacco related disease? only about 4 pack years

Yes: after only four pack years it is highly likely that whatever damage has been done will be undone, and that the lungs will remain healthy, and your risk of cancer, heart disease and other damage will return to baseline risks (which includes industrial exposures, second hand smoke, air pollution etc.). Congrats on the decision to quit, and PLEASE stick with it. It is difficult, but a good investment