Those are not counter examples, but entrepreneurship extremes. They just succeeded at first try (right time and place) while others either worked hard for long time or simply tried and failed few times.

I don't feel like the study shows something spectacular. Middle-age is the peak of performance, mental and physical health. Everything one created for himself is best seen at this peak and usually people start thinking what to do for the rest of their lives. Middle-age is not usually a time when you start having wild dreams.