You can quit man, YOU just have to decide to. I smoked from 16-30, couple of packs a day. I was a runner at the time and although I wasn't blazing fast I could cover a 5k in the mid 17's with whiskey on my breath haha. When I turned 30 almost 8 years ago, I just decided I didn't want to smoke anymore and quit. It sucked a bit but I did it and so can you. Friend of mine at work came out ten days ago with me, he's 47 and has smoked 30+ years and just decided he was done. Woke up Thursday morning and said no more, got on the plane and we flew out here to nowheresville and he's now on day 10 with no smoking. We work in a pretty high stress environment and if he can quit like that, I know you can.

Just do it, wait for all the crud to start coming up when you cough a few weeks after, and then watch how much better you feel.