>>95957533>I'm from US.fair enough
>I imagine it would be most popular among teens to mid twenties.That's two different demographics. For teens it's as you say - you're targeting their parents and need to sell it as reliable, trustworthy, and added value for the child's education. In that case it would work better if you work adjacent to school or other official institution (bigger cities should have some sort of "youths culture center", former komsomols).
For mid-20s (essentially people legally adult people out of highschool), you're targeting directly the customers, and better approach may be selling it as "cool" with the added value.
Another option to consider would be instead of D&D making it some sort of English Board Games Club, bigger initial investment to get the games (unless you already have a collection), but you don't care so much about player retention, people can come and go as convenient, and you don't need any prep time for each session.
Also, depending on which country you specifically reside at, you may need certification/permit to work with children. And be able to declare the income for tax purposes. (But I guess the friend that already teaches can fill you in on details.)