As then-17-year-old Sarah Melanson crossed the finish line of the ChesapeakeMan Ultra Championship early this fall, she couldn't believe what she had just endured.

She had swum 2.4 miles through jellyfish-infested waters, had biked 112 miles while battling near-record winds and then, to cap off a 15-hour effort, had run 26.2 miles for a full marathon.

"I was like, 'Are you sure I did that?'" Melanson said. "It was completely surreal. I couldn't even believe I had just done it."

Her disbelief was shared by the family members who gathered to watch her finish, long after darkness set on the dimly lit course in Cambridge in Dorchester County. Her mother, Cindy, cheered alongside her older sister, Emily. Her father, Mark, who ran triathlons while in college, was there, too, and later acknowledged that he wouldn't want to run that long.

Her boyfriend, Nicholas Caddenhead, a cyclist, was also supporting her — though unable to fathom how she could take on the running and swimming portions.

"I see it as a big accomplishment in my life," said Melanson, a 2013 South River graduate and freshman exercise physiology major at West Virginia. "I hope it serves as an inspiration to other people that there is no obstacle that can set you apart from your goals."

Robert Vigorito, a USA Triathlon-certified race director, said in an email that Melanson was the youngest female ever to complete the ChesapeakeMan. The race is organized by TriColumbia, the company he founded in 1986.

He also said that, because of sport-wide rules that usually prohibit runners under 18 from participating in ultratriathlons, Melanson was likely the youngest female entrant ever to complete that distance.

"I really would doubt that there are any others," Vigorito said.

Melanson signed a waiver to participate in the grueling race.

"I remember a 15-year-old boy did [a full Ironman Triathlon] a few years ago," Melanson said. "But I'm the youngest female, apparently."

Melanson joined the Annapolis Triathlon Club when she was 13, in 2008, after swimming competitively for a few years. Flipping through one of her father's photo albums, she became interested in the pictures of him racing. The family used to watch the televised Ironman World Championship, which she thought was "the coolest thing you could do."

Earlier this year, the club raffled off a half-price ticket ($75) to the ChesapeakeMan ultra triathlon. Melanson had thought about giving it a shot, so she entered her name.

"I said, 'Make sure you're prepared for it,'" Mark said. "This isn't a kid you have to push. If anything, you have to say, 'Why don't you take a break?'"

Club members were excited that someone so young would even consider that distance.

"People her age don't usually do that," Chrissy Fuentes, 56, said.

Michelle Faurot, 53, also a club member, competed in the world Olympic distance for her age group at the London Olympics in 2012. She met Melanson when the pair trained together during a weekly "Ladies Ride" hosted at Parvilla Cycles bike shop.

Back then, Melanson was riding on a bike formed from a conglomeration of her father's old bicycle's parts.

"There was Sarah, all of 14 at the time, riding this bike her dad had outfitted her out of stuff he had used almost 30 years ago. She had these old clipless pedals; they were really stiff," Faurot said. "I went back and told him after [the ride], 'Please buy your girl new pedals.'"

When it comes to triathlons, age is a number that doesn't create barriers.