Retirement systems around the world are expected to face a significant burden in the next 50 years. The number of people over the age of 60 is expected to double from 841 million in 2013, to over 2 billion by 2050, according to the UN. What's more this has been accompanied by falling global birth rates. In fact, the global share of people over the age of 60 has gone from 9.2% in 1990, to 11.7% in 2013 and is expected to hit 21.1% in 2050, according to Bank of America's Sarbjit Nahal and Beijia Ma. The number of people...