Her exact date of birth is not known.
Kim Yo-jong is a politician in her native North Korea.
The North also rolled out a variety of shorter-range solid-fuel missiles designed to be fired from land vehicles or submarines, which pose a growing threat to South Korea and Japan.
President Joe Biden on May 21 to maximize its political effect.
The pair are said to have a close relationship as a result of spending 1996 to 2000 studying in isolation together in Switzerland.
North Korea recently claimed to have test-fired a Hwasong-17 intercontinental ballistic missile Picture: AP South Korea Their most recent test-launch was of a solid fuel rocket.