That's one of the facets of rights, is the freedom to do things. Rights aren't only freedom from things.
And you might not like smoking, but other people are going to make choices and live their lives in ways you don't agree with, even that you abhor, and rights means you have to put up with that for the betterment of all.
So people, young people, are going to smoke, and you're going to put up with it.
Maybe you're not quite clear on what a right is - its generally something that that's enshrined in constitutional law like for example in a human rights act, or for some advanced democracies even the right to privacy is included in a bill of rights. The 'right to smoke and be unhealthy' is not a right at all, its a freedom that you may have.
No, rights are natural qualities, principles or states of being we are born with. They're either endowed by you by the creator of your choice or they exist through natural laws. They almost always can be derived from natural law and/or natural observation.
No human being dictates what rights another has, period. That means no, you don't get to tell people they don't have the right to smoke.
Grow the fuck up and accept that other people smoke and stop obsessing over things you can't control.
I'm in the natural law camp of people that understand the concept of natural rights, but good on you for making it obvious you have no real respect for rights.