Right, I have two answers for this one.

The earliest sign that I would be into vore despite having no concept of it was probably nursery age, 5 years old or lower. I recall the playground having this huge worm/caterpillar tunnel, with one end being its open mouth and the other being a nondescript backend. I used to spend a lot of my break times sitting inside that tunnel because it made me feel safe and content.

As for realising I liked vore itself, I'm positive that my first exposure to it was a sequence of Midna swallowing Navi that was uploaded to a forum I was frequenting. It was just a pencil sketch but I immediately found myself drawn to it. Since it was labelled as vore I figured I'd see if there was more of that kind of thing and that's how I found Eka's Portal and shortly thereafter e621 and Furaffinity.

My kink discovery has continued to this very day, but vore is the big one and has been ever since I saw that nice little Midna sequence.