I've seen fangirls on tumblr straight up get salty at the fact that Rogue wasn't gonna be in the movie. For them when it comes to Gambit, Rogue has to be there too. Otherwise what's the point.
Maybe a new rumor started up when all the stuff with the shoot date getting pushed back came out and they figured that an increased budget must mean that Rogue would be appearing somehow. Which is a huge leap in logic, but I wouldn't put it past someone to go there.
Speaking of a huge leap in logic, they did screw with the timelines so like they said, a lot of characters will be born sooner or later than they were in the original timeline, but we saw a glimpse into where this new timeline ends up and we clearly see Kitty, Colossus (even though he's in Deadpool and I'm starting to believe Deadpool takes place mid 90s), Iceman and yes, Rogue in no more than their early 30s.
So the idea of Rogue being born earlier and getting a new younger actress due to it, is out of the question... From a logical standpoint. In the end Fox may do whatever they want. I still think the only way we get Rogue and other X-Men in a future movie with Gambit being of similar age is time travel. Whether accidental or on purpose.
With the idea of creating their own connected universe ala MCU, Fox is pretty much going to have to handcuff Gambit to the current X-Men movies thus be stuck in the 80s or 90s for quite some time. Perhaps Gambit takes place several years after Apocalypse? But that would invalidate Fox's new young cast. Some of these kids are actually kids and wouldn't be able to pull off being anymore than 19-20 years of age.