Katie Ledecky dominates in the 800-meter freestyle at last summer’s Rio Olympics. (Jonathan Newton/The Washington Post)

Katie Ledecky was all of 15 years old when she won her first Olympic swimming gold and put the sport on notice that she’d be making some pretty big waves. The times are, no doubt, changing, evidenced by the pool prodigy’s attire Monday.

All decked out in Stanford gear on the eve of the U.S. nationals, Ledecky is 20, coming off her freshman year of college and spending most of her time living and training in California.

Her sport is growing up, too. After decades of inexplicable gender lines that barred women from competing at the longest distances, the International Olympic Committee finally added the women’s 1,500-meter race to its Olympic program, which has the swimming world buzzing about what might be possible for Ledecky at the Tokyo Games in 2020.

Ledecky won four golds and a silver at the 2016 Games, and that was without the 1,500, which is perhaps her most dominant race.

“I was happy to see it,” Ledecky said at a news conference Monday in Indianapolis. “I think adding the 1,500 was a long time coming. It’s good that there’s parity in the men’s and women’s distance events now.”

This week will provide the first real preview of what the push for Tokyo might look like. Ledecky is entered in the 100, 200, 400, 800 and 1,500 freestyle races at nationals, the prohibitive favorite in all but the shortest distance. Many eyes will be cast toward the 1,500, where she has upended the record books and posted some of her biggest victories.

Two years ago, before Ledecky became an Olympic darling or an NBC staple, the Bethesda native introduced the swimming world to the Ledecky Slam. She was the first swimmer ever — man or woman — to win the 200-, 400-, 800- and 1,500-meter freestyle races at a world championships.

It was big news around the pool deck but because it didn’t happen at an Olympics, the feat might’ve swam under the surface for some. Ledecky would go on to make history at the Rio Olympics a year later and suddenly has a chance to improve upon her medal haul in Tokyo and take the Ledecky Slam to an even bigger stage.

Ledecky could compete in at least six races in Tokyo — more if she decides to add the 400 individual medley, which she mostly uses as a training race, or somehow compete in a mixed relay, another event added to the Tokyo slate. The actual schedule of events could, of course, make an attempt at more than six races impossible. Only one female has ever won more than four golds at a single Olympics: East German swimmer Kristin Otto won six in 1988.

The sport has evolved since then, and Ledecky has many options to consider between now and Tokyo. While the sprints might have been considered more TV-friendly than the longer distances, Ledecky brings star power to the race and could allow networks to break for a commercial midrace and keep viewers glued to their seats for the race’s conclusion.

“I think it’s good that the sport isn’t static,” she said Monday. “The world isn’t static. If you look at the history of swimming, events have been added over time. Women had a lot fewer races back in the day.”

No one likely will benefit from the addition as much as Ledecky. She owns the six fastest 1,500-meter times ever. She first set the world record as a 16-year-old at the 2013 world championships. Two years later, at the 2015 world championships, she set a record in a qualifying heat, finishing nearly 30 seconds ahead of any other swimmer. One day later, she lowered that mark by more than two seconds to 15:25.48, nearly 15 seconds ahead of anyone else in the pool.

While the 1,500 will make its Olympic debut in 2020, it has been on the world championships program since 2001.

But because it wasn’t in Rio, Ledecky took a nearly-two-year break from the event, until the Arena Pro Swim Series earlier this month at Santa Clara, Calif. There were no signs of rust, as Ledecky posted a time of 15:35.65. Though slightly off the world-record pace, she was still more than 37 seconds ahead of anyone else and managed to post the world’s best time of the year.

She will have a busy few days in Indianapolis, and her performance this week will help determine the full slate of races she will attempt at the world championships next month in Budapest. The top two finishers in each race qualify for the U.S. squad that competes at worlds.

Repeating the Ledecky Slam is certainly not a given. Her nationals week kicks off with a 100-800 double Tuesday. And in Budapest, the grueling 1,500-meter race takes place on the same day as qualifying heats for the 200.

Ledecky, ever careful not to think past her next lap, would not speculate too much on how the Olympic additions might change her Tokyo program.

“Something I’ll have to talk to Greg about,” she said, referring to her Stanford coach Greg Meehan. “. . . Obviously, the 1,500 will have to be in the conversation now.”