I am supportive in principle, but I am curious as to the justification for this particular form of implementation. Is there any other law anywhere that works like this by banning something for all people born after a particular date forever?
Not that I know of. It's a drastic approach to be sure, but the rationale for it seems pretty clear to me. Quitting smoking is a fairly taxing process, and it would genuinely be kinda authoritarian for the state to force it on so many people. On the other hand, never picking up smoking is not something that negatively affects one's quality of life in any way (and of course is a net positive in the long run), so it makes sense to target people who are too young to have started smoking and make sure they never get the chance to.