I would rather not teach anyone but if they insist, you inform them about the implications and the addiction problem.
I would also advise against teaching gambling to under age people . I believe they can be easily affected by gambling problems.
Its not good to influence people to gamble, and if they insist you must tell them everything about gambling. Teenager are easily to influence, they should be guided by the right gambler or person so they can be prevented. Lets not encourage everyone to gamble, we know its risky.
For me there is nothing wrong with influencing people to gamble, as long as you yourself is a responsible gambler.
That way you will be able to teach them everything they need to know, games can easily be learn but the discipline is the most important thing every gambler must know.
Gambling in general is entertainment, so if you are having fun on it, I think it's good to share it with other people too.
Don't look only on the negative side as those who experience bad in gambling are only those who are irresponsible enough.