Welcome to my thread dedicated to strong, dominant women, age gaps and power struggles.
With those themes in mind, I would like to mention that the list of stories and ideas here is by no means exhaustive, and I'm open to most variations. Most of them can be played either as M/F or F/F, with the only restriction being that ( unless explicitly stated otherwise ) the male character has to be the less powerful ( but not necessarily outright submissive ) party, and although he doesn't have to be younger, he should certainly not be older.
With that said, on to the ideas.
Gladiatrix x Young Nobleman: Partly inspired by the show Spartacus, this story involves a gladiatrix - a female gladiator - and a young Roman nobleman. The nobleman can either be the son of the gladiatrix's owner, or a visitor who takes an interest in her, an interest the owner notices and seeks to take advantage of to gain political favor. She's obviously a strong woman, but is at least initially utterly obedient. Sexually, however, she would be on top.
Female Knight x Prince: She could be his bodyguard, or his trainer. Either way it's the story of a Prince or other young nobleman, and a strong woman. In this case, however, she can be the one who takes an interest in him, and she would have to be the dominant one in more ways than in the previous idea.
Amazonian Gym Teacher x Student: A modern take on the amazonian archetype. It's the story of a strong, dominant woman and a relatively weaker ( and younger ) man in a modern setting. It could either be a locker room one shot, or it could develop into something of a taboo relationship between the two.
Female Knight x Queen: A romance between a strong woman and her Queen, with less emphasis on the power difference between the two, and more of a taboo dimension. In this case, the Queen would likely be older by some ten - twenty years, but it can also be played the other way.
If any of this interests you, feel free to check my O/Os - and let me know!