ON "20/20 SATURDAY," JANUARY 19 ON ABC

Jazz is a typical 11-year-old girl except for one thing -- she was born as a boy. From the moment she could speak, Jazz sensed that she was trapped in the wrong body and decided to dress and live as a little girl. Her parents made the controversial decision to support her choice. ABC News started covering Jazz's story when she was five. Now, a tween, she stands at a new crossroads in her brave decision to define life on her terms: boys and dating, medicine and the ultimate surgery to become fully female. Jazz and her family speak candidly to Barbara Walters on "20/20 Saturday," JANUARY 19 (8:00-9:00 p.m., ET) on the ABC Television Network.

And: What happens to a family when a child's birth becomes a medical mystery? Walters updates a report on two vibrant young girls who suffer from a rapid aging disease called progeria, a fatal condition that currently affects 68 known children in the world. The disease causes children to age at 10 times the normal rate. It is incredibly rare - occurring in only one in four to eight million births. On average, children die by the age of 13. But now a breakthrough medical treatment is adding hope -- and hopefully even years -- to their lives. (OAD: 9/10/10)

Plus: Jay Schadler has the story of a paralyzed young man, his new wife and their unforgettable first wedding dance.

David Sloan is executive producer of "20/20."