It’s entirely reasonable to take regulatory steps to protect younger persons. Habits ingrained now last a lifetime - that’s why Juul is fighting this - a new generation of consumers is at risk of not having access to their product. Other cities and states are watching this play out.
By the way, just because you don’t see a lot of kids where you hang out, believe me there are tons of kids here. I have one. We live in San Francisco. There is a robust parent community here. You may not see it if you aren’t looking for it. For example, did you know there’s a large playground at ... mission Dolores park? And if you and your childless friends decided it was a fun place to play, you will get asked to leave. Possibly by the police.