The brain is not fully mature until adulthood, this is a fact. Sorry you find it an excuse.
And the anti-smoking zealots can be even more inconsiderate than a smoker. Believe me.
I'm not saying it isn't a fact I'm just saying it's the most bizarre excuse for the decision to smoke I've ever heard. I was a teenager once and had friends who smoked, why didn't I? Because I knew why it was stupid to, if I managed to put my undeveloped brain into gear for that I don't understand why others can't, otherwise wouldn't we have all started smoking as teenagers? There's no need for all these excuses, you smoke, fine, you have every right to, you don't need to justify that to me undeveloped brain or not- just don't do it around me or my child. We're not talking about people who don't smoke or anti-smokers we're talking about people who do and then pass on their disgusting, dangerous second hand smoke onto others including children.
I hope the number of us "anti-smoking zealots" continue to increase in numbers because the more smoking is irradiated the better it will be for our society and children, inconsiderate or not.