Eli Reimer is also possibly the first American teen with the syndrome - to have made the exceptional ascent last month, when he reached a staggering 17,600 feet after nearly two weeks of walking.
After walking for around 113 km, Reimer triumphed when he reached one of two base camps on the world's tallest mountain, 'New York Daily News' reported.
Eli's father, Justin Reimer, joined the teen last month along with their team setting out to raise money for the family's charity, The Elisha Foundation.
"It was surreal," Reimer told US news channel HLN in an interview. "To be standing there at that place and see the smile on Eli s face and the sense of accomplishment that he had, and the fact that his health was better than any of us at that point ... it was humbling, it was inspiring, just an amazing moment," said Reimer.
Atleast one more person with Down syndrome is known to have reached the base camp - a 35-year-old man from the UK, Justin Reimer told TIME magazine.
The father-son adventurer duo climbed nearly 17,600 feet to the mountain's south base camp in Nepal.
Eli's doctors gave him the thumbs-up to attempt the endurance-testing task, Reimer told the channel.
"We monitored his blood (saturation), oxygen saturation levels as we went up (the mountain).
"And his were consistently, significantly higher than everyone else's to where he was actually leading us on the trail.
Eli was like our guide on this whole thing," Reimer said.
"For anybody who has a child with a disability or who is impacted in some way ... the disability is not a limitation," said Justin Reimer, adding that Eli's life "and the lives of those with disabilities have infinite worth."
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