The father of a 13-year-old American who this week became the youngest person to climb Mount Everest on Wednesday defended the controversial expedition, saying it had gone "perfectly."

Jordan Romero reached the summit of Everest early Saturday, accompanied by his father Paul, setting a new record as the youngest ever to scale the world's highest peak.

Some mountaineers have said it was irresponsible to take such a young climber onto a mountain that has claimed the lives of many older and more experienced climbers.

"There's nothing irresponsible here. This young man was on top of the world. There's no faking it," Paul Romero, a paramedic, told AFP after crossing the border into Nepal from Tibet.

"We were so prepared, everything went absolutely perfectly. This was an amazing expedition. Age has nothing to do with anything," he said in his first face-to-face interview since the climb.

Jordan said the climb had been harder than he expected and admitted his knees were "a little bit sore."

But he said standing on top of Everest had been a "feeling like no other."

"It was very difficult. It was harder than I thought, definitely," he told reporters in the Nepalese border town of Liping, around 110 kilometres (70 miles) north-east of the capital Kathmandu.

"We were having the time of our lives, and it was the best view -- better than you can get anywhere in the world. A view of the world."

Romero, accompanied by his father and stepmother, reached the top of Mount Everest on one of the last days of the climbing season, which ended on Tuesday due to heavy snow.

Unlike many Western climbers, who join large, well-supported expeditions, Jordan and his family opted to scale the world's highest peak with just a small team of Sherpas to assist them.

Nepal does not grant permits for Everest to anyone under 16 and the family climbed the quieter north face of the mountain, in China, which does not impose age restrictions.

Many supporters have posted congratulations on Jordan's web site, but there has also been criticism of his expedition, with some mountaineers saying he was too young to assess the risks for himself.

Hundreds of people have died trying to climb Everest, many succumbing to injury or altitude sickness.

Jordan prepared for the trip by sleeping in a tent specially devised to simulate the effects of altitude, but medical experts have pointed out that there has been no research on the effects of oxygen deprivation on children.

The previous record holder was said to be Temba Tsheri of Nepal, who reached the peak aged 16, although there are reports that a 15-year-old Nepalese girl may also have made it to the summit.

Around 3,000 people have climbed Everest since Edmund Hillary and Tenzing Norgay became the first people to conquer the 8,848-metre (29,028-foot) peak in 1953.

The mountain lies on the border between China and Nepal and most people climb from the southern Nepalese side, which is generally deemed to be easier.

Around 250 people made it to the summit from the south side during the brief spring climbing season, which begins in late April and ends in late May, mountaineering officials have said.

Jordan climbed his first major peak, Kilimanjaro in Kenya, aged just 10, inspired by a mural showing the highest mountains on all seven continents.

His latest climb brought him a step closer to his goal of conquering all seven, and he now has just one -- the Vinson Massif in Antarctica -- to go.