Again, I have to (mostly) agree with Ace. I understand all about decreasing quality of life over time as a result of bad behavior, but Ace's point about genetics is equally valid. I've seen plenty of examples of people on either side of the issue. For example, one of my co-workers survived several heart attacks while in his 50s, and completely changed his life as result -- ate better, managed stress better, etc. Then, years later, over the course of just a few weeks, he started getting persistent headaches. Turned out to be a congenital brain tumor that no one had ever known about before that had started growing for some reason. He survived the immediate surgery but died 2 weeks later. One of my best friends is strong, healthy, physically active, doesn't drink or smoke, and mostly eats well but has genetically high cholesterol despite medication and diet. I won't be surprised if I outlive him.
Conversely, my grandfather spent most of his life drinking, smoking, and living badly. He survived into his 60s, but there's no question that his lifestyle contributed to the heart disease that eventually killed him, and he wasn't healthy at all in the last decade of his life. Ditto for my grandmother, who had emphysema and eventually died due to a collapsed lung and the incompetence of some healthcare workers.
So my lifetime creed is and has been for many years, "Moderation in all things, including moderation." Nikkoru, I do have a good 10 to 15 years on you, and I can tell you that my core outlook on life hasn't changed much since I was a teenager. I've picked up a few new dreams over time and given up on some others, but my beliefs haven't changed a lot. I have a streak of nihilism that I rarely bring up; with what I know of life today, I wouldn't be that upset if a rock hit me in the head tomorrow and killed me. So now my goal in life is to work hard to the point where I don't have to work anymore, then just basically goof off and enjoy myself as long as I can. But in the meantime I'm also going to enjoy myself while I'm still young and able to do so. I'm not going to be completely self-destructive, but I'm not going to live a harshly puritan life, either.