1971-83 are the phases from Capricorn to Gemini. It has 13 years for nine points. So each point is 13/9 = 1.45 years each. Capricorn, Aquarius & Pisces are two points each, or 2.89 years each.
As you can see Bill Gates enrolls at Harvard in the Capricorn phase of his life because Capricorn has to do with hard work and discipline… then drops out and starts Microsoft in the Aquarius phase of his life because Aquarius is the unstable, innovative kind.
1984-94 has four points spanning 11 years. Each point is therefore 11/4 = 2.75 years each.
Cancer, Leo and Virgo phases are one point each, or 2.75 years each. He becomes a millionaire and a billionaire in his Leo phase because Leo is the sign of excess and abundant success. Leo is the middle sign of the three summer signs, Cancer, Leo & Virgo, where maximum prosperity is found. He also has Jupiter (luck, prosperity) conjunct Pluto (force, transformation) in Leo.
He ends up sharing his wealth with his wife Melinda in the Scorpio/Sagittarius phases of his life because Scorpio is the sign of shared finances and Sagittarius is the sign of generosity and sharing as well as philanthropy and humanitarianism. Bear in mind this marriage eventually led to the foundation of the Bill & Melinda Gates Foundation.