as far as i know, he has always been musical, but he was trained primarily as a singer, with piano on the side, until he was about 16. then some professor who'se name i can't remember was really impressed with his playing and told him to focus on that instead. that was when the "serious study" began.
martha argerich says similarly- she didn't start playing "seriously" until she was 16, after winning that famous competition and playing mozart concerti at the age of ten, so to answer your question, they probably did have a lot of musical background, just compared to their own standards it was nothing much.
the less said of THEIR standards the better, else i'll get very depressed.