Cory H. answered 09/06/19
Fun, Engaging Tutor for English, Education, and Business
Hi there. The word "fast" refers to the fasts in Judaism, specifically the Fast of Gedaliah. It is associated with the fall of Jerusalem, although after all the fasts are complete, there is a return to happiness. The expression "Well over the fast" is wishing a future of happiness, which is a good thing to wish at a birthday party.
-Cory