Could you correct the mistakes I've made in this tiny essay about Bill Gates?
Bill Gates the American computer programmer, was one of the founders of Microsoft. In his teens he began to write software programs as a hobby. He hadn't finish school, when he studied, because he was expelled. While he was one of the creators of windows OS. He lived in California and with his team he made a new OS. He is the richest person on in the world, and he have has 5 children. His OS is the most popular one in the world and more then than half of the computers have windows OS installed.

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Bill Gates, the American computer programmer, is one of the founders of Microsoft.  (Is, since he's still alive.)  In his teens, he began to write software programs as a hobby (good).  He dropped out of Harvard after only two years of college.  (Expelled means that you are kicked out of school against your will; "drop out" means that you voluntarily choose to leave.)

He lived in California, and with his team made a new operating system (OS), called Windows.  He has five children, and is currently the richest person in the world.  Windows is the most popular OS in the world, being run on over half of all computers worldwide.