Finn is the son of Mace Windu
So if Finn is Force sensitive it is reasonable to think he might come from a Jedi lineage. Now if we believe that Mace Windu survives the attack on the Chancellor at the end of ‘Revenge of the Sith’ (which is another theory we will touch on) it is not too farfetched to think he would have a child after the fall of the Republic. This theory is a little flimsy, we admit, but it is noteworthy that Finn utilizes a very similar style of lightsaber combat that Mace was famous for using.