For a project I'm working on, a pair of "immortal" characters end up crossing from their dimension (a fantasy world) into what could be described as the "real" world, and I'm considering aging them back a bit when it happens. (Think "The Devil is a Part Timer" for that.) This would be because the 2 dimensions' timelines are moving at different speeds, instead of them being completely parallel. For example, Point A could be where they converge and are close enough to parallel that a portal could be opened and characters could cross over, while Point B could be 5 years later in one dimension and 50 years later in the other.
The characters are half vampire, so they'd age extremely slowly after reaching maturity, but they can still die under the right circumstances. For the story, I want to have them revert back to just before reaching maturity as humans when they cross into the other dimension. I'm trying to decide what would happen if they brought a human back with them into the fantasy dimension. I could explain some bits and pieces with the fact that there's no magic in the "real" world, but I feel like it would need something a bit extra to it.
Would the human age forward? Would they stay the same? Would they become a demi-god of some sort because 5 years for them is 50 years in the new dimension they're in?
Edit: looks like a lot of confusion is as to why their ages would be rolled back and I'm gonna chalk that up to them having magic in their blood or something and the other dimension they're entering having no magic, therefore their magic would've been removed upon entering the portal. The age change wouldn't be severe, it would probably be 5 year difference in appearance, or Something like that.