Oh, and sometimes even a single region has areas at different level ranges. For instance, after visiting the three main cities, you're sent to do a dungeon located in Western La Noscea, a region that's mostly around your level. Or about 2/3 of it or so is around your level at any rate. But in the western side of that region, beyond a pair of big gates, there's an area for players in their 40's. Whenever there's a big jump like that in level ranges within a single region, there will be a clear boundary marker (those gates I mentioned in this case) and NPC's who warn about tougher enemies beyond it.