Everyone does a few dumb things while they are teenagers. A frighteningly large number of teens (esp. here in France) start smoking. Choose something else, please!
It'd probably be better to get pregnant; we'll be here to help you stay in school etc., and having a kid can be quite a difficult commitment for a few years, but gradually gets easier. It will make some things harder in your life, but it won't generally shut many doors.
Starting smoking is a lifelong commitment that will never have a positive payoff beyond "hey a little buzz", has a decent chance of a fucking horrible cost (hello, young people with cancer) if you have the wrong genes, and relatively-horrible costs even if you don't (having a lower quality of life when you're old and dying younger, yes, but also the financial cost is staggering -- the cost of the cigarettes is just a bit of it; you'll pay more for health/homeowners/car/life insurance, everything you own and might re-sell will have lower value, if you start a fire like one of the hundreds of thousands of other smokers who do in any given year, you'll pay for that, etc.).
Or you may quit, and live the possibly-quite-unpleasant life of an addict who has quit their addiction. See above; it can suck intensely, and you will crumble, you will choose "worse life with" vs. "worse life without" and construct flimsy rationalizations around it, but the only winning move is not to play.
I lost two grandparents early to smoking-related illness/cancers, and I have a once-smoking friend who got lung cancer when she was 20, though she's still alive, so I can make sure they won't have any illusions about "the bad outcomes only happen to other people".
[huh, this didn't start as a rant, but it sure is one now.]