In its annual statistics, the UN's World Health Organization (WHO) said that six of the countries had even managed to raise life expectancy to over 10 years between 1990 and 2012.
The top achiever was Liberia, where average lifespans increased by a full 20 years, from 42 to 62.
Next in line were Ethiopia (from 45 to 64 years), Maldives (58 to 77), Cambodia (54 to 72), East Timor (50 to 66) and Rwanda (48 to 65).
Globally, average life expectancy rose by six years during the same period.
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Based on global averages, a girl who was born in 2012 can expect to live to around 73 years, and a boy to the age of 68, the WHO said.
"But there is still a major rich-poor divide: people in high-income countries continue to have a much better chance of living longer than people in low-income countries," Chan said.
For girls, the difference is even wider, with those in high-income countries likely to live to the age of 82 and those in poor nations to 63.
Female life expectancy in all the top 10 countries of the globe is 84 years or more, the WHO said.
Women in Japan enjoy the world's best life expectancy, at 87 years, followed by Spain, Switzerland and Singapore on 85.1 years each.
"In high-income countries, much of the gain in life expectancy is due to success in tackling noncommunicable diseases," said Ties Boerma, head of the WHO statistics division.