For as long as he can remember, Andrew Miller has felt at home in the mountains, on trails and in the woods.

All his life he’s backpacked with his family, sometimes for a week at a time in the rugged mountains of the Pacific Northwest and California’s Sierra Nevada. His idea of fun is scrambling up rocky slopes and looking for the next peak to conquer.

“I just like being outside like that for a long time and enjoying nature,” says Miller, from Corvallis, Ore.

It’s one of two reasons he says he fell in love with ultrarunning. The other?

“Just seeing how much I can push myself, and how well I can do,” he says.

So far, Miller has done quite well, pushing himself to unexpected heights. At just 20 years old, he’s on an ultra roll, winning three straight races and five of his past seven.

But it was his most recent victory, in California’s Western States 100-Mile Endurance Run on June 24, that earned attention.

Miller became the youngest winner in the history of America’s oldest 100-mile race, winning its 42nd edition in 15 hours, 39 minutes. In just his second 100-miler, Miller went in with a strategy and stuck with it.

“My angle was just to run fairly comfortably for most of the first half and try to run well for the second half, pick up the pace a little maybe, and try to catch some guys,” says Miller, who is a member of Salomon’s elite trail running team.

As the miles wound down, the strategy was working. Miller was in the top 10 after Mile 40 when he quickened his stride. He kept picking off runners and at one point thought he’d finish second. Leader Jim Walmsley seemed uncatchable, way out front on a record pace. But Walmsley took a wrong turn with about 20 miles to go and Miller took advantage. Once in the lead he got a burst of energy and cruised home with the win far ahead of runner-up Didrik Hermansen of Norway (16:16:08).

In a sport in which many of the best runners are in their 30s and 40s—he was one of only two twentysomethings in the top 13 men—Miller had by far his biggest victory. The sport has gotten younger in recent years with the likes of Anton Krupicka, Dakota Jones, Pete Kostelnick and Kilian Jornet among those who have turned the sport on its head in recent years. But none started off so successfully at such a young age.

“I definitely think most people were surprised I won, yeah,” he says, laughing. “Not a lot of people—I guess a few from back home—knew I was running pretty well and feeling pretty good. But yeah, I’d say 95 percent of the ultra community probably had no clue I was running as well or feeling as good as I was.”

RELATED: Pete Kostelnick Eyes the Ultimate American Running Record

Figuring it out

Andrew and his younger brother, Jacob, have followed in the footsteps of their mother, Anne, a self-described “midde-of-the-pack” ultrarunner. The boys used to follow her on their bikes when she went on training runs, then started tagging along on foot.

At 14, Andrew ran his first ultra with his mom, the McKenzie River 50K, finishing 117th in 6:13:26. The next year he did the McDonald Forest 50K with her, running 6:17:32.

“For some reason, it was after that second one that I was hooked,” he says. He recalls thinking, “I really want to do this.”

It was about that time Anne could see her son’s potential. Because of his age, race directors required mother and son to run together. By the second race she says, “I was probably holding him up.”

Miller played three years of soccer in high school, but didn’t run cross country or track. He preferred to run on his own. At 16, he won his first ultra, the McKenzie River 50-miler in 7 hours, 12 minutes. By 18, he had won a handful of 50- to 100-kilometer races, as well as the 68-mile Georgia Death Race in early 2015.

Since June of 2015 he won the Bighorn 100-miler, setting a record of 18:29:37, and then the Georgia Death Race again in March of this year to earn a spot at Western States.

He says he’s “figured it out” the past two years.

He’s learned what training works best for him. He went from doing mostly long, slow runs to adding a lot of shorter, faster workouts.

“I’ve never done any traditional speed work, like going to the track, but I’ll do some hill repeats, or just run hard up a hill or two or three hills in a run, just to get running faster,” says Miller, who works his training around classes and homework at Northern Arizona University in Flagstaff. “I really think adding that variety, not only to get the speed but also to get your body to adapt to a lot of different types of running, has really helped.”

Plus, Miller is an analytical sort. He likes to study and prepare. Anne Miller says by the time her son was at the starting line for Western States, he knew the history of every top runner there and where on the course he planned to go hard or take it easy.

“Andrew does nothing that’s not calculated,” she says.

He’s also an exercise science major, entering his sophomore year. That’s helped him better understand how his body functions in training and during the middle of a run.

Miller is looking next at the North Face 50-miler in December. Between now and then, he might also take a crack at trying to break Rob Krar’s best-known time of 6 hours, 21 minutes, 47 seconds in running the 42-mile rim-to-rim-to-rim route at the Grand Canyon.

“We’ll see how I’m feeling,” he says. “He ran a really, really fast time.”

At 5-foot-4 and about 125 pounds, Miller isn’t imposing by any means. Other top ultra marathoners are taller, older or have more experience. But he believes his preparation and mindset are his strengths. He actually embraces the pain that sets in late in races when his legs and mind are exhausted.

“You want to quit but it’s kind of fun to overcome that and tell yourself to keep going,” he says. “It’s fun to take on that challenge and convince yourself to keep going … to keep running fast.

“When it all comes together at the end, if you can finish strong, finish well and be happy with your run, it’s just really cool.”

RELATED: Generation Next: Influential and Inspiring Runners Under 30