There is no "right" to buy tobacco. The government can certainly regulate the age at which someone can purchase tobacco, especially given the health risks to tobacco use. While you can always consult with attorneys who are familiar with government regulatory issues, I doubt you have a case to pursue...
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Any lawyer who handles litigation can represent you. This case will cost you thousands of dollars to persue.
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There is frivolous legal action you could take that is expensive and won't survive summary judgment. If you want to light up at 18 move to less of a nanny state.
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If you were able to find enough people willing to join you in a "class action" suit, maybe - but it's a very expensive proposition. And, since there's no money to be won, no attorney is going to take it on any sort of contingency fee basis. Therefore, for practical purposes, it's not worth pursuing. Reminds of of when I was around your age and the drinking age went from 18 to 19, then to 21. Many of my friends lost the right to drink in NY. It was there tough luck, but rest assured, they did not stop drinking.
I'm just 3 "helpful" answers away from a free toaster-oven! I may be guessing or not licensed in your state. No atty/client relationship exists.