I think that in the past smoking has been in my family, so the reason most of my siblings and I probably tried it was for a couple reasons - 1) we saw it happen in the family and wanted to try it ourselves, and 2) none of us really tried it until college, and then many of us became social smokers and then some, habitual smokers because of that.
After I tried it, and after some time, I found I liked smoking for a few reasons. First of all, there's of course the fact that you get a buzz, and I like that. Then, I just really enjoy taking a few moments to relax, think about life, and watch the smoke.
Then, if alcohol is involved, the buzz from smoking is even more for me, which is nice. Then, if friends are involved, there is the added enjoyment of being with friends and nice discussions.
By the way, I am 23. I do not smoke a lot, though - precisely because I know it damages my health. The most I ever habitually smoked was probably 4-5 cigarettes per day average, and that was for a period of 2-3 months. In the last year of my life, I have probably averaged 1-2 cigarettes per day. So I guess if I am damaging my health, I suppose I'm not taking years and years off my life span, just a few. :) I guess my brain, still not fully formed as a 23-year old, is just trying to tell me that the small amount of time my life might be decreased is worth it, for the enjoyment I get from smoking.