CapnZapp
Legend
Sorry, no.You can use the NPC method to represent something with less effort than statting out a full PC, but that doesn't mean you can or should represent things that are clearly in defiance of how people exist in the world. It would be disingenuous to create an NPC wizard who had 7th-level spells and only 5 hit dice, because that shows a disconnect between levels and what they mean.
The laws of the world are that you need a certain amount of experience in the world before you can wield that powers of a Dragonmark (except for humans, if you're using that one overpowered variant). If you let NPCs get away with this, where PCs cannot, then your players have every right to call you out on this.
Rule #1 of being a good DM: Be fair. The PCs might not be special snowflakes who can break the rules of the world, but neither are the NPCs.
The corollary to npcs don't break rules is npcs must follow rules.
And it is positively fantastic that 5e allows you to make a 5 hit dice NPC with more than third level spells!