Examples of top academics who weren't prodigies
Thomas Kuhn literally switched fields after completing his PhD in physics and is a modern philosopher well known for his work in the philosophy of science, particularly for his book The Structure of Scientific Revolutions

Karl Pearson, may be another example. Although he initially studied mathematics and then physics, he proceeded onto other things like law before eventually switching back to mathematics and making his big contributions (like establishing mathematical statistics). I have not been able to find anything immediately obvious to indicate he was a child prodigy.

As an ecologist, I'd hazard to guess that most famous ecologists were never child prodigies, but they almost certainly identified their passions early on in life while playing outside as children, which violates the


  before finding their passion in a field


part of your question.