Not sure what you mean by early leverage given he used virtually no leverage throughout his career. Insurance float is basically the only form he's used and didn't start that until the middle of his career.

His annualized returns running the Buffett Partnerships with zero leverage were close to 40% per year for the dozen or so years they were operating.

And everyone compounds gains just by holding index funds for long periods. Buffett compounds them far faster because he has substantially higher returns than the market.