I thought this would be an easy question. Until I tried answering it. I grew up among plants, but finding a specific "first cause" is trickier than I thought.
Unlike some people who say they recall being toddlers, or even babies, my earliest recollections are from about 3 years old and those mostly involve learning to tie my shoes and such. My earliest plant memories involve grapevines where I got stung by wasps. Not a good start!
But I recall my paternal Grampa's garden at about 6. He had more space planted in beans then I have lawn. And that was just the start. There was corn, there was tomatoes, there was strawberries, raspberries, blackberries, melons, etc, etc, etc. And he was organic back in the 50s.
And then there was Dad, who thought he knew better. He covered the garden of kale and potatoes with 30-30-30 stuff. The kale tasted like tin cans and the potatoes were always damaged digging them up in the clay soil. And he sprayed the apple tree so often the apples tasted like tin cans too.
I liked Grampa's garden a WHOLE lot better than Dad's. So I became organic. Anywhere! I swear, I grew more "edible" veggies on a west-facing apartment balcony in ten 5 gallon pots than Dad ever did in his drenched clay soil garden of 500 sq ft!
The amazement of fresh-tasting tomatoes, cucumbers, and red bell peppers and pole beans has addicted me ever since then!