There are a few out there. It's difficult to find them that are experienced enough to give training that is robust, due to a young age limiting the amount of experience they were able to garner.

Another reason you don't find as many younger male Dominants is for the most part men take a while to mature enough to understand what it is they are looking for, and so hit that early to mid thirties range before they even begin to look. There are exceptions of course.

Female Dommes who are young are around, but even more rarely so. I'm not sure why that is, but I think it has something to do with how many male submissives are out there, and so they really don't have to put themselves out there to much to find what they want.

You're best bet is if your not looking for online is to try your local group, and use the contacts there.