Kuala Lumpur, May 10: Veteran Malaysian leader Mahathir Mohamad, a former Prime Minister who led the opposition to achieve a stunning victory in the general election, took the oath of office on Thursday.Mahathir, who governed for more than two decades became, at the age of 92, the world s oldest elected leader. Supporters waved flags and cheered outside the Istana Negara palace here as he took the oath inside.The ceremony was witnessed by Malaysia s Head of State Sultan Muhammad V. A statement released by the royal palace ahead of the ceremony said the Sultan invited Mahathir to form the next federal government.