I was able to enter the area on a level 190 that had previously learned the summon familiar spell while being 200+.
Any other character below 200 I tried was not able to gain access with the npc saying "15:45:09 Phillip: Please find the monster before it hurts anyone. But remember, this is a very dangerous task. You should be sure to have some assistance, preferably from a familiar you can trust."
It appears the requirement is tied to having learned the summon familiar spell in the past rather than a current level requirement. This would align with the rest of the quest where your summon is "stolen".
I would encourage someone 200+ without familiar spell to try and gain access before purchasing the spell to confirm.