I think a 12-year age difference with the gal being older is reason enough to disregard that possibility. LOL
That aside, what seems to be an issue for everyone is that there was no explanation for the couple. This confuses me because:
1. It's a shonen action series; romance is tertiary at best.
2. Kishimoto clearly has no knack for anything remotely romantic.
3. There is naturally going to be a lot not covered when you have a huge gap in time like that between 699 and 700.
4. Choji's a secondary character, so it's unreasonable to expect his story to be covered in any meaningful way. And Karui is even less than secondary. Yes, you could say the same for ShikaTema, but they have had the whole series to build up little moments of direct and meaningful interactions. When would Choji and Karui have had time between her introduction as an antagonist and them being in different divisions during the war? Also, people don't have to meet as teens to have a meaningful relationship.
So I'm sorry if I don't find the argument, "They came out of nowhere" a particularly justifiable one when it comes to deriding this couple. Really, where was any relationship for Choji going to come from but nowhere?
To be fair, he had a modicum of interaction with Ino to suggest that he really cares for her. Recall he was consoling her when she was crying over Sasuke being labled a traitor to the leaf. There are a few other scenes as well come to think of it.