Why do investors need to know about the central banking system? Have the banks learned anything from the 2008 market crash? Neil Irwin, The New York Times economic correspondent and author of The Alchemists: Three Central Bankers and a World on Fire, discusses whether the economy is on the verge of another crash, the impact of having banks that are considered "too big to fail", and how the central banking system affects the decisions of individual investors. When planning your investments or for retirement, you don't only need to look at the central banking system, but also at the circumstances in your own life, such as your age. Doug gives focused investment advice on how to plan for retirement when you are in your 30s, 40s, and 50s. Find out how your age affects your risk level, what kind of expenses you may have, and the best kinds of investments for you, depending on your age. Follow Neil Irwin at: www.nytimes.com/section/upshot and on Twitter @Neil_Irwin