February
I had this problem too on the PS4. I had my teen throw numerous parties and got gold on the parties, and none of them triggered the 'achieve gold on a hosted party'. Very frustrating and now she has automatically aged up already.
She hosted a potluck, 2 birthdays, a charity event and a family reunion. Got gold on all of them.
I have all the expansion packs except werewolves and vampires.