A、At the age of 20. B、By the age of 12. C、When he was at high school. D、When he studied in Harvard University. B

Bill Gates was born in Seattle, Washington in 1955. He co-founded Microsoft in 1975 with Paul Allen, his high school friend and partner in computer-language development since 1967.
    Fascinated by computers by the age of 12, Gates was involved with various programming projects throughout high school. While attending Harvard in 1975, Gates teamed with Allen to develop a version of the BASIC computer-programming language for the Altair, the first personal computer. As a result of this work on BASIC, Gates decided to drop out of Harvard in 1977 to work at Microsoft full-time, pursuing his vision of "a computer on every desk and in every home," the idea behind the company. In the early 1980s, Gates led Microsoft’s evolution from a developer of programming languages to a diversified software company producing operating systems and applications software as well as programming tools. This transition began in 1981 with Microsoft’s introduction of MS-DOS, the operating system for International Business Machines Corporation’s new Personal Computer. Gates persuaded other computer manufacturers to standardize on MSDOS, fueling software compatibility and computer industry growth in the 1980s. Gates also pushed Microsoft to introduce application software, such as Microsoft Word word-processing software for the IBM PC. In a key strategic move, Gates agreed to develop application software for the Apple Macintosh prior to the release of the first Mac in 1984. This was the beginning of strong position for Microsoft in applications that take advantage of the graphical user interface.
    Much of Gates’ success rests on his ability to translate technical visions into market strategy, and to blend creativity with technical acumen. He is one of the few founding CEOs from the technical side of the PC industry who has also survived and thrived on the business side.