Mine probably was when I took a job as a baker at a local restaurant/deli in high school. First day in, I was handed a neat little stack of laminated index cards for things like muffins, cookies, tarts, etc.
Before that, I had simply cooked by watching others (mostly my parents), or just by trial and error.
Up until then, the thought of using a recipe to cook something was completely foreign to me.
Even to this day, I find recipes to be more of an impediment than a resource, much less a necessity.
You? When did you first use a recipe to cook something? And do you find recipes all that necessary in your cooking?