KATHMANDU (AFP) - A Sherpa aiming to conquer Everest for the 18th time and septuagenarians battling for the title of oldest climber to reach the summit are lining up their record bids as the main climbing season opens. Nepal this week lifted a climbing ban imposed to prevent pro-Tibet protests on the roof of the world as the Chinese Olympic torch was carried up the northern approach to the mountain from Tibet. The main season for climbing the world's highest peak is expected to open towards the end of this month and hundreds of mountaineers, support staff and paying clients from 32 expeditions are now acclimatising for the final push. "Now because of climate change, the season is shifting later and later. This year we expect the good weather window might open around the third week of May," said Ang Tsering Sherpa, chairman of the Nepal Mountaineering Association and an expedition organiser. With a breathtaking 17 summits of the 8,848-metre (29,028-foot) peak already under his belt, Apa Sherpa looks likely to get to the top again, said chairman Ang Tsering."I think Apa has a good chance. He is physically very, very fit and as long as the weather permits, he will break his own record," he said.Last year, retired Japanese school teacher Katsusuke Yanagisawa 71 years and two months old when he reached the summit became the oldest man to conquer the peak. This year two men are trying to beat the record. His countryman, 75-year-old adventurer Yuichiro Miura is currently at base camp struggling with acclimatisation a process of making short trips up and down the lower reaches of the mountain to prepare climbers for the "death zone" above 8,000 metres, where there is just a third of the oxygen present at sea level. "I was tired all day yesterday," Miura wrote on his expedition website Friday. "But then I remembered it was the same situation as when I was 70 years old, but I feel even more tired now than when I was here when I was 70," said Miura, who won international fame in 1970 when he became the first person to ski down the South Col of Mount Everest, using a parachute as a brake. Despite his previous Himalayan exploits which also include clinching the record for the world's oldest person atop Everest in 2003 Miura is up against stiff competition in 77-year-old Nepalese Min Bahadur Sherchan. Sherchan is a former British Gurkha soldiers who have been part of the British army for nearly 200 years and was a government mountaineering liaison officer with years of experience of high peaks. "When I last spoke with him he said he is feeling in very good condition," Ramjindaji Gurung, coordinator of Sherchan's Senior Citizen Mount Everest Expedition, told AFP.