NEW DELHI: Paytm founder Vijay Shekhar Sharma , 39, is the youngest Indian billionaire , while 92-year-old Samprada Singh , chairman emeritus of Alkem Laboratories , is the oldest, according to Forbes Sharma, ranked 1,394th on the list with a fortune of USD 1.7 billion, is the only Indian billionaire in the under-40 league.Sharma founded fast-rising mobile wallet Paytm in 2011. He has also created Paytm Mall, an e-commerce business business and Paytm Payments Bank "One of the biggest beneficiaries of India's demonetisation, Paytm has notched up 250 million registered users and 7 million transactions daily. Sharma owns 16 per cent of Paytm, which is now valued at USD 9.4 billion," Forbes said.Of the 2,208 billionaires in Forbes' 2018 list of the world's richest, just 63 are under the age of 40 and more than half (34) are self-made entrepreneurs.In all, the 63 youngest billionaires in the world are worth a collective USD 265 billion, up from USD 208 billion last year.Meanwhile, 92-year-old Samprada Singh, who is the chairman emeritus of Alkem Laboratories, is the oldest Indian billionaire. He was ranked 1,867th on the list with a fortune of USD 1.2 billion.Singh founded the pharma firm Alkem Laboratories 45 years ago. Singh worked in a chemist's store before venturing out on his own distributing pharmaceuticals."Shares of the generics maker, known for its antibiotics Clavam and Taxim, have more than doubled since its November 2016 IPO. For the year ended March 2017, Alkem reported a 20 per cent rise in net earnings to USD 139 million on revenues of USD 913 million," Forbes said.