Bill Gates (Jin Lee/Bloomberg)

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Bill Gates arguably has time on his side at age 54, but his focus on donating his wealth to worthy causes suggests his net wealth figure will be heading in the wrong direction to attain $1 trillion. Still, if Mr. Gates were to live to be 90 years old and chose to refocus his efforts once again on wealth accumulation, it would take annual growth of about 8.5 per cent to reach $1 trillion — the first candidate on our list with a goal that seems attainable.

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