Microsoft Co-founder Bill Gates' wealth has hit the $100 billion mark, making him a centibillionaire and the only second person besides world's richest person, Amazon Founder Jeff Bezos, with $100 billion wealth, Bloomberg said on Wednesday. Amazon's 55-year-old Founder is now worth $145.6 billion after adding $20.7 billion to his wealth this year. Microsoft's 63-year-old Gates gained $9.5 billion.