I believe that people can call themselves whatever they want. I call myself a slave, whereas I know to some people I would not be considered as much because I don't adhere to certain rules. Or I have been with my Daddy for less than 2 years or some other reason.

I have no problem with what others want to call themselves (or what the other person in their relationship to call them). I won't be addressing random people as the Grand Pooba just because that's what (s)he feels their position ought to be called.

I don't think there is any requisite age or experience level attached to Master or Sir or Daddy or Grand Pooba or Grand Dictator of the Universe. If that's what gets your jollies going to be called, that's between you and the other people in your relationship.

Expert I feel a little differently on. I feel like if you are using the title of expert you are probably trying to teach other people something or are lecturing or something, and I do feel like you should have a fair amount of experience in whatever you are claiming to be an expert at. That's just me.