I started when I was 14 and built up to almost 3 packs a day when I quit at age 43. That was 8 years ago and though I know any damage that was going to be done is already there I know I'm not going to make it any worse and get a financial reward from it as well.
I quit cold turkey, I think it was the fear factor, I had just had a TIA and wife-ack ranged in. I was lucky all of my cravings vanished in 3 days, at first I couldn't be around smokers but now I don't mind it if it's just one or two of them, any more than that and I find it hard to breathe.