Started about 14, quit about 40 (in 1988), haven't touched tobacco since.
My advice to quitters is basically forget tapering off and all that crap. I tried all sorts of things, and the only thing that worked was to quit cold and stick to it. It also helps to change other things at the same time. Start exercising, break patterns. The really hard part I found was in situations that have always been associated with lighting up, and tend to trigger it - stopping to think about a mechanical problem, talking on the phone, the first cup of coffee in the morning, etc. There's no easy answer. It's difficult. I knew it was stupid, expensive, ugly and dangerous, but I still enjoyed smoking. But at some point you have to decide who is boss: you or the habit.
One of the things that helped me, aside from marrying a non-smoker, was to get serious about bicycling. You just can't get up those steep Vermont hills with lungs full of smoke.