I started smoking when I was 12 and quit when I was 23. 10.5 years at 2 packs of a day of red's. Got a bad cold where I couldnt breathe right for two days straight and I didnt smoke for those two days. After I started feeling better I thought to myself that I could have a smoke. Then I realized I didnt smoke for two days, handed my pack over to my brother and that was it. 7 years later I haven't had one since. The worst part for me was the first two weeks, after that it was easy to cope with.
As for someone who said about stunting growth. Im 6'4".
I dont think that it affected me to much.
Just as it was said before, it is a matter of making your mind up doing something and sticking to it. Now if I could do the same with the gym...