You are right. It is different for everyone. I smoked intermittently in my late teens and early twenties - never more than a few weeks at a time. At one time I was even receiving free samples of cigarettes. The last time I stopped smoking I found it more difficult than the previous times, so I thought, "Bugger this!" I haven't smoked cigarettes since 1981.
   My mother finally stopped smoking in her early forties after several failed attempts. My father stopped at the first attempt in his late forties after some thirty years.
   My girlfriend, then 27, stopped smoking within the first month of us living together. (I never said anything - so I have always wondered what it was about me that put her off her ciggies). If I return from an evening of passive smoking (rehearsal room/pub etc), I am greeted with the tender words, "You stink!" It's all encouragement. Nothing like stopping my nookie to keep me on the straight and narrow!