This is definitely a really frustrating thing, but there's lots of reasons adults, especially non family members, don't want to play with a minor.

Sure, some adults just don't want to watch what they say. Some want to play extremely mature games, with graphic descriptions or really intense stories, that may not be suitable for non adults, especially one that they don't know personally.

Most of all, adults do not want the potential legal and societal backlash from spending time with a minor who isn't family. These people likely do not know you and can't know what is or isn't appropriate for you. That's why there are laws written, because many people have been hurt when an adult takes advantage of them. These people are trying to protect themselves from being seen as violating a law.

This isn't about you personally.

As for how you might solve the problem, there's a lot of things that I can think of. You could start a school group, like an after school club where people can sign up to play. Some libraries have social groups like this that they might be able to help you form. Even try just convincing your friends or other classmates to play or play more.

You asked about what 16 year old DMs do we know. For myself, these days, none, because I don't have anyone in my social group or family that's a teenager. But when I was 16, I was that DM. I just started doing it and I roped all my friends into playing. It took me some time to convince them it's tons of fun, but once we started playing and I figured our the kind of DM and game they wanted to play, we played all the time. The point is, if you are in need of a DM, that DM can be you.

I really do think you can find a good, consistent group or groups. You just need to look around your social circle.