The DC to create a magic item increases by +5 for each prerequisite the caster does not meet.
Creating a magic weapon has a special prerequisite: The creator's caster level must be at least three times the enhancement bonus of the weapon.
So, I'm pretty sure you don't need to be that level to craft it. You just raise the DC by 5.
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That would be a Craft DC of 30 without the requirement, it's not super easy to say the least.
But anyway:
It depends what kind of caster you are dealing with. There are so many options and customization nowadays, that knowing why your spellcaster made a particular choice when it comes to their options or received his gifts would help shape the personality and ambience of the meeting.
A witch with a deception patron, a forgepriest (cleric archetype with artifice domain), A sorcerer with the nanite bloodline or an abjurer for example, already can change the tone of the roleplay encounter. This doesn't even take into account their alignment and various other factors.
Worst come to worst, you can always use the random background generator from ultimate campaign, it should give you a good idea of where the npc comes.
I guess if you make an item that casts a 9th level spell with every metamagic feat the spell level would be 101, needing a CL of 201 to craft. That being said, you can craft items if you don't have the right CL; it's just an extra +5 to the spellcraft DC.
*Edit: lol ninja'd on the +5 to spellcraft DC
Anything above 11th level are heroes of myth and legends. Think of characters like Merlin, Hercules, or Belgarath. Each one should be unique and have a well-established role in their world.