At just 18 years old, Nepali mountaineer Nima Rinji Sherpa is on the brink of a remarkable achievement.

With 13 of the world's highest peaks already behind him, he is now one summit away from becoming the youngest person to conquer all 14 mountains towering above 8,000 metres (26,247 feet).

Sherpa, who already holds multiple records from his ascents of dozens of peaks, said he is on a mission to "inspire a new generation and redefine mountaineering".

His final challenge, Shishapangma in Tibet, awaits him next month -- if China issues a permit.

Summiting all 14 "eight-thousanders" is considered the epitome of mountaineering aspirations.

Italian climber Reinhold Messner first completed the feat in 1986, and only around 40 climbers have successfully followed in his footsteps. Many other elite climbers have died in the pursuit. 

All of the mountains are in the Himalayas and neighbouring Karakoram range, which span Nepal, China, India and Pakistan.

Reaching each summit requires entering the thin air of the "death zone", where there is not enough oxygen to sustain life for long.

"When I am in the mountains, I may die anytime," Sherpa said. "You need to realise how important your life is."

The young man says the mountains have taught him to stay calm.

"Mentally, I have convinced myself... when I see an avalanche, bad weather, an accident in the mountains I am not in a hurry, I don't get nervous," he added.

"I have convinced myself; this is normal in the mountains. I think this has helped me a lot."