Who’s a Medicare expert? Anyone by law, no one in reality

I have never liked the word ‘expert’. It feels imprecise and poorly defined, like knowing exactly when to enter a roundabout.
What makes an expert? Experience? Education? Both?
Paul Keating left school at the age of 14 but went on to be hailed as the world’s best finance minister.
Does that make him an expert economist or simply someone with innate economic talent? Is there a difference?