I would love to see these two get together. Search #CHARLOE on Twitter or Charloe on YouTube and you'll see that the ship for these two is fairly wide spread. I agree that the actors have amazing chemistry with each other. I am fairly surprised by how many people have a negative reaction to the idea of this pairing.
Is it the age thing? That's silly. These guys live in a very different world than we do. Regardless of age, they have to be tough and strong. They have to be self sufficient and adaptable. They are living off the land. They frequently have to kill people (with swords! even) to protect themselves. How could age matter at all?
Is it the 'but he killed her Dad and Danny' thing? I don't like that argument either. Yes, he was partially responsible, but I think others share that responsibility. Ben's death: Danny should have just shut up when Neville came for Ben. If he'd done that, Ben might have went peacefully and not have died at all. Danny's death: Monroe's men killed Danny - but it wasn't a persoanl thing. He was a casualty of war. Also, Rachel made the amplifier that fueled the helicopter. If we're going to point fingers willy-nilly, one probably needs to be pointed her way.
All that said, the pickings are slim with this group for any romantic mash ups. Most of them are related to each other. These two make an obvious pairing. I'm not a fan of Jason (crazy and untrustworthy) or Connor (too immature - merely a less vivid version of his father - that Happy Endings encounter was such a mistake)... so why wouldn't Charlie go for Monroe and vice/versa? They are both smokn hot and the way that they look at each other is pretty intense even when they're angry. Nobody can stay mad forever. Eventually I think sparks will fly.
I know that David and Tracy have said some stuff in interviews that makes it sound like CHARLOE will never happen, but I think the writers might give us some hope yet. We shall see.