With this I just want to say that I know it's a difficult task but presenting it as a lost battle/impossible seems to me wrong.
"Peers’ smoking is the strongest predictor of adolescent smoking."[1]
[1] Gecková, A.M., Stewart, R., van Dijk, J.P., Orosová, O.G., Groothoff, J.W. and Post, D., 2005. Influence of socio-economic status, parents and peers on smoking behaviour of adolescents. European addiction research, 11(4), pp.204-209.
The thing is, we made headway in the battle against smoking by disallowing people from doing all those things. You're not allowed to market to kids, you're not allowed to depict smoking in most TV that kids are likely to watch, you're not allowed to smoke in or near schools and teachers who do are frowned upon. Cigarettes themselves are taxed heavily specifically to price young people out of getting into the habit, vendors are required to card, and the cigarette makers are even required to pay into a fund that promotes anti-smoking messaging.
So yes it is definitely not an impossible task. But the things that make it possible require taking it seriously as a danger and addressing it collectively.
> But I was taught not to do it and never did it.
So not all young people in your time were taught similarly. Or if they were, those teachings didn't stick.
Ideally the number of minors smoking would be zero. I don't think that's a radical idea, and I hope it's something that everyone can agree on. "Teachings from parents" obviously didn't achieve that goal, from your own experience.