Of the two teenage Americans who won gold medals Friday at the London Games, one came into the Games with expectations of greatness—Missy Franklin. But the other impressed just by making the Games in the first place.

Katie Ledecky, a 15-year-old from Bethesda, Md., is two years younger than Franklin but years ahead of her time. She just finished her freshman year at Stone Ridge (High) School of the Sacred Heart.

Now she is an Olympic champion in the 800-meter freestyle.

At the U.S. Olympic Trials, she won the 800 with the second-fastest time in the world this year (see video here). She also finished third in the 400 free, narrowly missing out on being in two events in London. She was one place away from qualifying for the 200 free finals at trials as well.

This had already been a breakout year for Ledecky, but with her gold medal, it's a year beyond anyone's imagination.

If fans hadn't heard of her before the Games, that was partly by design.

Coach Yuri Suguiyama has held tightly onto her reins despite knowing that she was an advanced swimmer. He said he doesn’t like to rush the development process.

“Katie could have skipped some steps, but she has learned from each experience and still moved up the competitive ladder,” he said (via NBC; link above). “Some people questioned us not taking her to Nationals last summer, but I think it was great that she was able to go to Juniors, win four races and win the high-point award.”

At the 2011 Junior National Championships, Ledecky won the 1,500 free, 800 free and 400 free and finished fourth in the 200 free and 25th in the 100 free. Although she is primarily a distance swimmer, Ledecky has the speed to be competitive in shorter races as well.

If Ledecky's story sounds somewhat familiar, it’s because of the last 15-year-old swimmer from Maryland who qualified for the Olympics in 2000, finishing fifth in the 200 fly. His name is Michael Phelps.

In Ledecky’s younger days—of which there haven’t been many—she dreamt of the Olympics, but it always seemed far off. She told the media at the trials (via The New York Times):

“Four years ago, I never knew how to qualify for an Olympic trials. I thought it was an unreal thing. It’s just unbelievable to think back at where I was and think about the work I’ve put in these last couple of months with my coach, Yuri Suguiyama. He’s really prepared me, and I had a lot of confidence.”

She may swim a confident race, but she is also quiet and nervous in front of the media. Not many 15-year-olds are used to that kind of spotlight, but Ledecky is far from a normal 15-year-old.

“I’m not into much pop 15-year-old kind of things,” she said in a video interview with Yahoo! Sports (see right), where she also mentioned that she doesn’t even have her driving learner’s permit yet.

Now she is one of a select group of swimmers who've won an Olympic gold medal before learning how to drive.