There is nothing wrong having those fantasies or wanting to act them out, many people share your fantasies. What sets red flags off here is the age difference and the proposed situation. There is nothing wrong with age differences in relationships, however the fact you are so young, makes me worry he might be taking advantage of that. Does this man know you are underage? I don't think a dom/sub relationship would be the best thing for you, especially at this age and when you are just getting out in the world and learning more about yourself. You deserve to be free to explore the world and focus on obtaining an education, which you sound very motivated and determined to obtain. There is nothing wrong with being sexual, or exploring your sexuality, but it's best to do it with people you know, feel safe with and are going to treat you with respect, even in a dom/sub situation, or roleplay, something about this guy you describe makes me worry he wouldn't be able to do that.