I remember learning what hunger feels like; I was probably around 8 years old. It's not that I hadn't had those sensations before. I just hadn't consciously made the connection between the sensations and the amount of time since my last meal, thoughts of food, etc.

Incidentally, more recently I've refined my hunger-related sensations. In particular, when I'm under stress I often tense my abdominal muscles which can lead to[1] sensations that are similar to hunger pangs, with predictable results. Intentionally relaxing those muscles and paying closer attention lets me discern which sensations are due to hunger (low blood sugar or empty stomach) and which are due to stress.

[1] Though actually, I'm not sure if that's the correct causality.