Is it true that if you quit smoking before age 30 the risk of diseases reduced almost completely? does the body clean & repair itself after quitting?

Risk reduced: Completely, i dought! yes the body doe try ; cleanse itself as you stated.

lung cleaning: Smoking paralizes the "mucocilliary elevator, " a slow upward flow of mucus from the lungs to help remove particles too big for white blood cells to "eat" and dispose of. Can take a week to a month per year of regular smoking to "clean house." you have to do the rough math, since tobacco usually heavier use than mj. Lungs will work better and be healthier when process is done!