Brooke Greenberg died of Syndrome X aged 20 having never aged She's shown me that as hard as it gets sometimes, the next day it can only get better ... Brooke Greenberg's father Howard. Picture: WBALTV Source: Supplied A WOMAN who never aged has died. Brooke Greenberg, of Reisterstown, Maryland, looked and behaved like a toddler until her last breath. "She literally is the fountain of youth if you think about it," Howard Greenberg told NBC. She's shown me that as hard as it gets sometimes, the next day it can only get better. Brooke was eventually diagnosed by her physician with "Syndrome X," an unidentifiable and unexplained rare disease - which is known to affect only about six people in the world - where they do not age physically or mentally since early childhood. "While the outside world may have noticed Brooke's physical stature and been puzzled by her unique development state, she brought joy and love to her family," Rabi Andrew Busch, who delivered the eulogy at the funeral yesterday, told the New York Daily News. Her parents, three sisters and extended family showered her with love and respected her dignity throughout her entire life. Never aged ... Brooke Greenberg has died aged 20 from an unknown condition that meant she never aged from beyond a child. Picture: WBPF Source: Supplied Brooke and her family appeared on Katie Couric's talk show in the US in January. They said Brooke could not talk, had baby teeth and still had to be pushed aboutn in a chair. From age one to four, Brooke changed. She got a little bit bigger. But age four, four to five, she stopped," her father told Katie. Brooke was born a month premature, weighing 1.814kg. She needed surgery for an anterior hip dislocation but it was only when her younger sister aged beyond her that her parents realised something was amiss. The parents took her to specialist after specialist who were unable to diagnose her condition. Dr Eric Schadt, director of Icahn Institute for Genomics and Multiscale Biology at New York's Mount Sinai Medical Centre, said that Brooke had "no apparent abnormalities in her endocrine system, no gross chromosomal abnormalities, or any of the other disruptions known to occur in humans that can cause developmental issues." Her parents bought a casket and clothes for her funeral after being told repeatedly that Brooke was going to die. "The older she gets, the more unbelievable it gets," her mother, Melanie Greenberg, told TV station WBAL in 2005.