Office workers rush past, oblivious to the army of grey-haired residents toiling in the shadows of Hong Kong's soaring skyscrapers.Dragging trolleys laden with waste, they sell whatever they can collect for just a few dollars.Hong Kong is home to 64 billionaires and has the highest number of Rolls-Royces per capita in the world.But one in three elderly people lives in poverty - one of the highest senior poverty rates in the developed world.And with a rapidly ageing population, Hong Kong could soon face a 'silver tsunami'.101 East asks why so many elderly residents are struggling to survive in one of the world's richest cities.