Zimbabwe's 92-year-old President Robert Mugabe should step aside without delay and allow new leadership of a country whose political and economic implosion since 2000 is dragging down the whole of southern Africa, Botswana President Ian Khama said. Despite his reputation as one of Africa's most outspoken figures, Khama's remarks are certain to raise hackles in Harare, where factions of Mugabe's ruling ZANU-PF party are locked in a bitter struggle to succeed the only leader Zimbabwe has known. Asked by Reuters if Mugabe, who came to power after independence from Britain in 1980, should accept the reality of his advancing years and retire, 63-year-old Khama responded: "Without doubt. He should have done it years ago." "They have got plenty of people there who have got good leadership qualities who could take over," Khama, the UK-born son of Botswana's first president, Seretse Khama, and his British wife, Ruth, continued. "It is obvious that at his age and the state Zimbabwe is in, he's not really able to provide the leadership that could get it out of its predicament," Khama said, in comments that breach an African diplomatic taboo banning criticism of fellow leaders. Botswana, the world's largest producer of diamonds, shares 800…