That's a good question. It seems like scripted enemies aren't generally scaled to your level. Places like Saugus Ironworks have higher level enemies and if you go there at a low level you might not make it through. But if you clear it out and come back a few days later, generic NPCs spawn in place of the scripted ones and are scaled to your level. The same is true with places like Gunner's Plaza and the Quincy Ruins, as well as various super mutant locations. It seems like anywhere with a named NPC is level locked until it's been cleared once, at which point the respawning enemies are leveled.
My current character is level 123, so there isn't going to be much of a challenge even if enemies are scaled. I'm starting a new character when the new survival mode comes out, and that's likely the character I'll use for all of the DLC.